Nanostructured carbon-metal oxide composite electrodes for supercapacitors: a review

Science.gov (United States)

Zhi, Mingjia; Xiang, Chengcheng; Li, Jiangtian; Li, Ming; Wu, Nianqiang

2012-12-01

This paper presents a review of the research progress in the carbon-metal oxide composites for supercapacitor electrodes. In the past decade, various carbon-metal oxide composite electrodes have been developed by integrating metal oxides into different carbon nanostructures including zero-dimensional carbon nanoparticles, one-dimensional nanostructures (carbon nanotubes and carbon nanofibers), two-dimensional nanosheets (graphene and reduced graphene oxides) as well as three-dimensional porous carbon nano-architectures. This paper has described the constituent, the structure and the properties of the carbon-metal oxide composites. An emphasis is placed on the synergistic effects of the composite on the performance of supercapacitors in terms of specific capacitance, energy density, power density, rate capability and cyclic stability. This paper has also discussed the physico-chemical processes such as charge transport, ion diffusion and redox reactions involved in supercapacitors.

Nanostructured carbon-metal oxide composite electrodes for supercapacitors: a review.

Science.gov (United States)

Zhi, Mingjia; Xiang, Chengcheng; Li, Jiangtian; Li, Ming; Wu, Nianqiang

2013-01-07

This paper presents a review of the research progress in the carbon-metal oxide composites for supercapacitor electrodes. In the past decade, various carbon-metal oxide composite electrodes have been developed by integrating metal oxides into different carbon nanostructures including zero-dimensional carbon nanoparticles, one-dimensional nanostructures (carbon nanotubes and carbon nanofibers), two-dimensional nanosheets (graphene and reduced graphene oxides) as well as three-dimensional porous carbon nano-architectures. This paper has described the constituent, the structure and the properties of the carbon-metal oxide composites. An emphasis is placed on the synergistic effects of the composite on the performance of supercapacitors in terms of specific capacitance, energy density, power density, rate capability and cyclic stability. This paper has also discussed the physico-chemical processes such as charge transport, ion diffusion and redox reactions involved in supercapacitors.

Methods of making metal oxide nanostructures and methods of controlling morphology of same

Science.gov (United States)

Wong, Stanislaus S; Hongjun, Zhou

2012-11-27

The present invention includes a method of producing a crystalline metal oxide nanostructure. The method comprises providing a metal salt solution and providing a basic solution; placing a porous membrane between the metal salt solution and the basic solution, wherein metal cations of the metal salt solution and hydroxide ions of the basic solution react, thereby producing a crystalline metal oxide nanostructure.

Observations of the Kondo effect and its coexistence with ferromagnetism in a magnetically undoped metal oxide nanostructure

Science.gov (United States)

Sapkota, Keshab R.; Maloney, F. Scott; Wang, Wenyong

2018-04-01

In this work, we report unusual observations of Kondo effect and coexistence of Kondo effect and ferromagnetism in indium tin oxide (ITO) nanowires that were synthesized without incorporating any magnetic impurities. The temperature-dependent resistivity (ρ -T ) data exhibited an upturn below 80 K and then tended to saturate below 10 K. The ρ -T and magnetoresistance data were analyzed using the n -channel Kondo model, and from the obtained values of S =1 and n ˜1 , the nanowires were expected to be an underscreened Kondo system. A model was also proposed to explain the formation of localized S =1 spin centers in the ITO nanowires. This work could provide insights into the understanding of spin-related novel phenomena in metal oxide nanostructures.

Magnetic layering transitions in a polyamidoamine (PAMAM) dendrimer nano-structure: Monte Carlo study

Science.gov (United States)

Ziti, S.; Aouini, S.; Labrim, H.; Bahmad, L.

2017-02-01

We study the magnetic layering transitions in a polyamidoamine (PAMAM) dendrimer nano-structure, under the effect of an external magnetic field. We examine the magnetic properties, of this model of the spin S=1 Ising ferromagnetic in real nanostructure used in several scientific domains. For T=0, we give and discuss the ground state phase diagrams. At non null temperatures, we applied the Monte Carlo simulations giving important results summarized in the form of the phase diagrams. We also analyzed the effect of varying the external magnetic field, and found the layering transitions in the polyamidoamine (PAMAM) dendrimer nano-structure.

Nanostructured Metal Oxides for Stoichiometric Degradation of Chemical Warfare Agents.

Science.gov (United States)

Štengl, Václav; Henych, Jiří; Janoš, Pavel; Skoumal, Miroslav

2016-01-01

Metal oxides have very important applications in many areas of chemistry, physics and materials science; their properties are dependent on the method of preparation, the morphology and texture. Nanostructured metal oxides can exhibit unique characteristics unlike those of the bulk form depending on their morphology, with a high density of edges, corners and defect surfaces. In recent years, methods have been developed for the preparation of metal oxide powders with tunable control of the primary particle size as well as of a secondary particle size: the size of agglomerates of crystallites. One of the many ways to take advantage of unique properties of nanostructured oxide materials is stoichiometric degradation of chemical warfare agents (CWAs) and volatile organic compounds (VOC) pollutants on their surfaces.

Facile conversion of bulk metal surface to metal oxide single-crystalline nanostructures by microwave irradiation: Formation of pure or Cr-doped hematite nanostructure arrays

International Nuclear Information System (INIS)

Cho, Seungho; Jeong, Haeyoon; Lee, Kun-Hong

2010-01-01

We report a method for converting the surfaces of bulk metal substrates (pure iron or stainless steel) to metal oxide (hematite or Cr-doped hematite) nanostructures using microwave irradiation. When microwave radiation (2.45 GHz, single-mode) was applied to a metal substrate under the flow of a gas mixture containing O 2 and Ar, metal oxide nanostructures formed and entirely covered the substrate. The nanostructures were single crystalline, and the atomic ratios of the substrate metals were preserved in the nanostructures. When a pure iron sheet was used as a substrate, hematite nanowires (1000 W microwave radiation) or nanosheets (1800 W microwave radiation) formed on the surface of the substrate. When a SUS410 sheet was used as a substrate, slightly curved rod-like nanostructures were synthesized. The oxidation states of Fe and Cr in these nanorods were Fe 3+ and Cr 3+ . Quantitative analyses revealed an average Fe/Cr atomic ratio of 9.2, nearly identical to the ratio of the metals in the SUS410 substrate.

Magnetic anisotropy of two-dimensional nanostructures: Transition-metal triangular stripes

International Nuclear Information System (INIS)

Dorantes-Davila, J.; Villasenor-Gonzalez, P.; Pastor, G.M.

2005-01-01

The magnetic anisotropy energy (MAE) of one-dimensional stripes having infinite length and triangular lateral structure are investigated in the framework of a self-consistent tight-binding method. One observes discontinuous changes in the easy magnetization direction along the crossover from one to two dimensions. The MAE oscillates as a function of stripe width and depends strongly on the considered transition metal (TM). The MAE of the two-leg ladder is strongly reduced as compared to that of the monoatomic chain and the convergence to the two-dimensional limit is rather slow

Metal Oxide Nanostructures in Food Applications: Quality Control and Packaging

Directory of Open Access Journals (Sweden)

Vardan Galstyan

2018-04-01

Full Text Available Metal oxide materials have been applied in different fields due to their excellent functional properties. Metal oxides nanostructuration, preparation with the various morphologies, and their coupling with other structures enhance the unique properties of the materials and open new perspectives for their application in the food industry. Chemical gas sensors that are based on semiconducting metal oxide materials can detect the presence of toxins and volatile organic compounds that are produced in food products due to their spoilage and hazardous processes that may take place during the food aging and transportation. Metal oxide nanomaterials can be used in food processing, packaging, and the preservation industry as well. Moreover, the metal oxide-based nanocomposite structures can provide many advantageous features to the final food packaging material, such as antimicrobial activity, enzyme immobilization, oxygen scavenging, mechanical strength, increasing the stability and the shelf life of food, and securing the food against humidity, temperature, and other physiological factors. In this paper, we review the most recent achievements on the synthesis of metal oxide-based nanostructures and their applications in food quality monitoring and active and intelligent packaging.

Metal oxide nanostructures: preparation, characterization and functional applications as chemical sensors.

Science.gov (United States)

Zappa, Dario; Bertuna, Angela; Comini, Elisabetta; Kaur, Navpreet; Poli, Nicola; Sberveglieri, Veronica; Sberveglieri, Giorgio

2017-01-01

Preparation and characterization of different metal oxide (NiO, WO 3 , ZnO, SnO 2 and Nb 2 O 5 ) nanostructures for chemical sensing are presented. p-Type (NiO) and n-type (WO 3 , SnO 2 , ZnO and Nb 2 O 5 ) metal oxide nanostructures were grown on alumina substrates using evaporation-condensation, thermal oxidation and hydrothermal techniques. Surface morphologies and crystal structures were investigated through scanning electron microscopy and Raman spectroscopy. Furthermore, different batches of sensors have been prepared, and their sensing performances towards carbon monoxide and nitrogen dioxide have been explored. Moreover, metal oxide nanowires have been integrated into an electronic nose and successfully applied to discriminate between drinking and contaminated water.

Physicochemical and Electrophysical Properties of Metal/Semiconductor Containing Nanostructured Composites

Science.gov (United States)

Gerasimov, G. N.; Gromov, V. F.; Trakhtenberg, L. I.

2018-06-01

The properties of nanostructured composites based on metal oxides and metal-polymer materials are analyzed, along with ways of preparing them. The effect the interaction between metal and semiconductor nanoparticles has on the conductivity, photoconductivity, catalytic activity, and magnetic, dielectric, and sensor properties of nanocomposites is discussed. It is shown that as a result of this interaction, a material can acquire properties that do not exist in systems of isolated particles. The transfer of electrons between metal particles of different sizes in polymeric matrices leads to specific dielectric losses, and to an increase in the rate and a change in the direction of chemical reactions catalyzed by these particles. The interaction between metal-oxide semiconductor particles results in the electronic and chemical sensitization of sensor effects in nanostructured composite materials. Studies on creating molecular machines (Brownian motors), devices for magnetic recording of information, and high-temperature superconductors based on nanostructured systems are reviewed.

Polymer derived non-oxide ceramics modified with late transition metals.

Science.gov (United States)

Zaheer, Muhammad; Schmalz, Thomas; Motz, Günter; Kempe, Rhett

2012-08-07

This tutorial review highlights the methods for the preparation of metal modified precursor derived ceramics (PDCs) and concentrates on the rare non-oxide systems enhanced with late transition metals. In addition to the main synthetic strategies for modified SiC and SiCN ceramics, an overview of the morphologies, structures and compositions of both, ceramic materials and metal (nano) particles, is presented. Potential magnetic and catalytic applications have been discussed for the so manufactured metal containing non-oxide ceramics.

Benzyl Alcohol-Mediated Versatile Method to Fabricate Nonstoichiometric Metal Oxide Nanostructures.

Science.gov (United States)

Qamar, Mohammad; Adam, Alaaldin; Azad, Abdul-Majeed; Kim, Yong-Wah

2017-11-22

Nanostructured metal oxides with cationic or anionic deficiency find applications in a wide range of technological areas including the energy sector and environment. However, a facile route to prepare such materials in bulk with acceptable reproducibility is still lacking; many synthesis techniques are still only bench-top and cannot be easily scaled-up. Here, we report that the benzyl alcohol (BA)-mediated method is capable of producing a host of nanostructured metal oxides (MO x , where M = Ti, Zn, Ce, Sn, In, Ga, or Fe) with inherent nonstoichiometry. It employs multifunctional BA as a solvent, a reducing agent, and a structure-directing agent. Depending on the oxidation states of metal, elemental or nonstoichiometric oxide forms are obtained. Augmented photoelectrochemical oxidation of water under visible light by some of these nonstoichiometric oxides highlights the versatility of the BA-mediated synthesis protocol.

Mesoporous Transition Metal Oxides for Supercapacitors.

Science.gov (United States)

Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

2015-10-14

Recently, transition metal oxides, such as ruthenium oxide (RuO₂), manganese dioxide (MnO₂), nickel oxides (NiO) and cobalt oxide (Co₃O₄), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO₂, MnO₂, NiO, Co₃O₄ and nickel cobaltite (NiCo₂O₄), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and aresnides

Energy Technology Data Exchange (ETDEWEB)

Das, Supriyo [Iowa State Univ., Ames, IA (United States)

2010-01-01

Oxide compounds containing the transition metal vanadium (V) have attracted a lot of attention in the field of condensed matter physics owing to their exhibition of interesting properties including metal-insulator transitons, structural transitions, ferromagnetic and an- tiferromagnetic orderings, and heavy fermion behavior. Binary vanadium oxides VnO_2n-1 where 2 ≤ n ≤ 9 have triclinic structures and exhibit metal-insulator and antiferromagnetic transitions.[1–6] The only exception is V₇O₁₃ which remains metallic down to 4 K.[7] The ternary vanadium oxide LiV₂O₄ has the normal spinel structure, is metallic, does not un- dergo magnetic ordering and exhibits heavy fermion behavior below 10 K.[8] CaV₂O₄ has an orthorhombic structure[9, 10] with the vanadium spins forming zigzag chains and has been suggested to be a model system to study the gapless chiral phase.[11, 12] These provide great motivation for further investigation of some known vanadium compounds as well as to ex- plore new vanadium compounds in search of new physics. This thesis consists, in part, of experimental studies involving sample preparation and magnetic, transport, thermal, and x- ray measurements on some strongly correlated eletron systems containing the transition metal vanadium. The compounds studied are LiV₂O₄, YV₄O₈, and YbV₄O₈. The recent discovery of superconductivity in RFeAsO_1-xF_x (R = La, Ce, Pr, Gd, Tb, Dy, Sm, and Nd), and AFe₂As₂ (A = Ba, Sr, Ca, and Eu) doped with K, Na, or Cs at the A site with relatively high T_c has sparked tremendous activities in the condensed matter physics community and a renewed interest in the area of superconductivity as occurred following the discovery of the layered cuprate high T_c superconductors in 1986. To discover more supercon- ductors

Building Composite Fe-Mn Oxide Flower-Like Nanostructures: A Detailed Magnetic Study

KAUST Repository

Zuddas, Efisio; Lentijo Mozo, Sergio; Casu, Alberto; Deiana, Davide; Falqui, Andrea

2017-01-01

Here we show that it’s possible to produce different magnetic core-multiple shells heterostructures from monodispersed iron oxide spherical magnetic seeds by finely controlling the amount of a manganese precursor and using in a smart and simple way a cation exchange synthetic approach. In particular, by increasing the amount of precursor we were able to produce nanostructures ranging from Fe3O4/Mn-ferrite core/single shell nanospheres to larger, flower-like Fe3O4/Mn-ferrite/Mn3O4 core-double shell nanoparticles. We first demonstrate how the formation of the initial thin manganese-ferrite shell determines a dramatic reduction of the superficial disorder in the starting iron oxide, bringing to nanomagnets with lower hardness. Then, the growth of the second and most external manganese oxide shell causes the magnetical hardening of the heterostructures, while its magnetic exchange coupling with the rest of the heterostructure can be antiferromagentic or ferromagnetic, depending on the strength of the applied external magnetic field. This response is similar to that of an iron oxide-manganese oxide core-shell system but differs from what observed in multiple-shell heterostructures. Finally, we report as the most external shell becomes magnetically irrelevant above the ferrimagnetic-paramagnetic transition of the manganese oxide and the resulting magnetic behavior of the flower-like structures is then studied in-depth.

Building Composite Fe-Mn Oxide Flower-Like Nanostructures: A Detailed Magnetic Study

KAUST Repository

Zuddas, Efisio

2017-07-21

Here we show that it’s possible to produce different magnetic core-multiple shells heterostructures from monodispersed iron oxide spherical magnetic seeds by finely controlling the amount of a manganese precursor and using in a smart and simple way a cation exchange synthetic approach. In particular, by increasing the amount of precursor we were able to produce nanostructures ranging from Fe3O4/Mn-ferrite core/single shell nanospheres to larger, flower-like Fe3O4/Mn-ferrite/Mn3O4 core-double shell nanoparticles. We first demonstrate how the formation of the initial thin manganese-ferrite shell determines a dramatic reduction of the superficial disorder in the starting iron oxide, bringing to nanomagnets with lower hardness. Then, the growth of the second and most external manganese oxide shell causes the magnetical hardening of the heterostructures, while its magnetic exchange coupling with the rest of the heterostructure can be antiferromagentic or ferromagnetic, depending on the strength of the applied external magnetic field. This response is similar to that of an iron oxide-manganese oxide core-shell system but differs from what observed in multiple-shell heterostructures. Finally, we report as the most external shell becomes magnetically irrelevant above the ferrimagnetic-paramagnetic transition of the manganese oxide and the resulting magnetic behavior of the flower-like structures is then studied in-depth.

Mesoporous magnetic secondary nanostructures as versatile adsorbent for efficient scavenging of heavy metals

Science.gov (United States)

Bhattacharya, Kakoli; Parasar, Devaborniny; Mondal, Bholanath; Deb, Pritam

2015-01-01

Porous magnetic secondary nanostructures exhibit high surface area because of the presence of plentiful interparticle spaces or pores. Mesoporous Fe3O4 secondary nanostructures (MFSNs) have been studied here as versatile adsorbent for heavy metal scavenging. The porosity combined with magnetic functionality of the secondary nanostructures has facilitated efficient heavy metal (As, Cu and Cd) remediation from water solution within a short period of contact time. It is because of the larger surface area of MFSNs due to the porous network in addition to primary nanostructures which provides abundant adsorption sites facilitating high adsorption of the heavy metal ions. The brilliance of adsorption property of MFSNs has been realized through comprehensive adsorption studies and detailed kinetics. Due to their larger dimension, MFSNs help in overcoming the Brownian motion which facilitates easy separation of the metal ion sorbed secondary nanostructures and also do not get drained out during filtration, thus providing pure water. PMID:26602613

Carbon and oxide nanostructures. Synthesis, characterisation and applications

Energy Technology Data Exchange (ETDEWEB)

Yahya, Noorhana [Universiti Teknologi PETRONAS, Tronoh, Perak (Malaysia). Dept. of Fundamental and Applied Sciences

2010-07-01

This volume covers all aspects of carbon and oxide based nanostructured materials. The topics include synthesis, characterization and application of carbon-based namely carbon nanotubes, carbon nanofibres, fullerenes, carbon filled composites etc. In addition, metal oxides namely, ZnO, TiO2, Fe2O3, ferrites, garnets etc., for various applications like sensors, solar cells, transformers, antennas, catalysts, batteries, lubricants, are presented. The book also includes the modeling of oxide and carbon based nanomaterials. The book covers the topics: - Synthesis, characterization and application of carbon nanotubes, carbon nanofibres, fullerenes - Synthesis, characterization and application of oxide based nanomaterials. - Nanostructured magnetic and electric materials and their applications. - Nanostructured materials for petro-chemical industry. - Oxide and carbon based thin films for electronics and sustainable energy. - Theory, calculations and modeling of nanostructured materials. (orig.)

Advanced Magnetic Nanostructures

CERN Document Server

Sellmyer, David

2006-01-01

Advanced Magnetic Nanostructures is devoted to the fabrication, characterization, experimental investigation, theoretical understanding, and utilization of advanced magnetic nanostructures. Focus is on various types of 'bottom-up' and 'top-down' artificial nanostructures, as contrasted to naturally occurring magnetic nanostructures, such as iron-oxide inclusions in magnetic rocks, and to structures such as perfect thin films. Chapter 1 is an introduction into some basic concepts, such as the definitions of basic magnetic quantities. Chapters 2-4 are devoted to the theory of magnetic nanostructures, Chapter 5 deals with the characterization of the structures, and Chapters 6-10 are devoted to specific systems. Applications of advanced magnetic nanostructures are discussed in Chapters11-15 and, finally, the appendix lists and briefly discusses magnetic properties of typical starting materials. Industrial and academic researchers in magnetism and related areas such as nanotechnology, materials science, and theore...

Mesoporous Transition Metal Oxides for Supercapacitors

Science.gov (United States)

Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

2015-01-01

Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors. PMID:28347088

Mesoporous Transition Metal Oxides for Supercapacitors

Directory of Open Access Journals (Sweden)

Yan Wang

2015-10-01

Full Text Available Recently, transition metal oxides, such as ruthenium oxide (RuO2, manganese dioxide (MnO2, nickel oxides (NiO and cobalt oxide (Co3O4, have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO2, MnO2, NiO, Co3O4 and nickel cobaltite (NiCo2O4, and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

A general strategy toward the rational synthesis of metal tungstate nanostructures using plasma electrolytic oxidation method

Energy Technology Data Exchange (ETDEWEB)

Jiang, Yanan; Liu, Baodan, E-mail: baodanliu@imr.ac.cn; Zhai, Zhaofeng; Liu, Xiaoyuan; Yang, Bing; Liu, Lusheng; Jiang, Xin, E-mail: xjiang@imr.ac.cn

2015-11-30

Graphical abstract: A general strategy for the rational synthesis of tungstate nanostructure has been developed based on plasma electrolytic oxidation (PEO) technology (up). Using this method, ZnWO{sub 4} and NiWO{sub 4} nanostructures with controllable morphologies and superior crystallinity can be easily obtained (down), showing obvious advantage in comparison with conventional hydrothermal and sol–gel methods. - Highlights: • Plasma electrolyte oxidation (PEO) method has been used for the rational synthesis of tungstate nanostructures. • ZnWO{sub 4} nanoplates have strong mechanical adhesion with porous TiO{sub 2} film substrate. • The morphology and dimensional size of ZnWO{sub 4} nanostructures can be selectively tailored by controlling the annealing temperature and growth time. • The PEO method can be widely applied to the growth of various metal oxides. - Abstract: A new method based on conventional plasma electrolytic oxidation (PEO) technology has been developed for the rational synthesis of metal tungstate nanostructures. Using this method, ZnWO{sub 4} and NiWO{sub 4} nanostructures with controllable morphologies (nanorods, nanosheets and microsheets) and superior crystallinity have been synthesized. It has been found that the morphology diversity of ZnWO{sub 4} nanostructures can be selectively tailored through tuning the electrolyte concentration and annealing temperatures, showing obvious advantages in comparison to traditional hydrothermal and sol–gel methods. Precise microscopy analyses on the cross section of the PEO coating and ZnWO{sub 4} nanostructures confirmed that the precursors initially precipitated in the PEO coating and its surface during plasma discharge process are responsible for the nucleation and subsequent growth of metal tungstate nanostructures by thermal annealing. The method developed in this work represents a general strategy toward the rational synthesis of metal oxide nanostructures and the formation mechanism of

A general strategy toward the rational synthesis of metal tungstate nanostructures using plasma electrolytic oxidation method

International Nuclear Information System (INIS)

Jiang, Yanan; Liu, Baodan; Zhai, Zhaofeng; Liu, Xiaoyuan; Yang, Bing; Liu, Lusheng; Jiang, Xin

2015-01-01

Graphical abstract: A general strategy for the rational synthesis of tungstate nanostructure has been developed based on plasma electrolytic oxidation (PEO) technology (up). Using this method, ZnWO 4 and NiWO 4 nanostructures with controllable morphologies and superior crystallinity can be easily obtained (down), showing obvious advantage in comparison with conventional hydrothermal and sol–gel methods. - Highlights: • Plasma electrolyte oxidation (PEO) method has been used for the rational synthesis of tungstate nanostructures. • ZnWO 4 nanoplates have strong mechanical adhesion with porous TiO 2 film substrate. • The morphology and dimensional size of ZnWO 4 nanostructures can be selectively tailored by controlling the annealing temperature and growth time. • The PEO method can be widely applied to the growth of various metal oxides. - Abstract: A new method based on conventional plasma electrolytic oxidation (PEO) technology has been developed for the rational synthesis of metal tungstate nanostructures. Using this method, ZnWO 4 and NiWO 4 nanostructures with controllable morphologies (nanorods, nanosheets and microsheets) and superior crystallinity have been synthesized. It has been found that the morphology diversity of ZnWO 4 nanostructures can be selectively tailored through tuning the electrolyte concentration and annealing temperatures, showing obvious advantages in comparison to traditional hydrothermal and sol–gel methods. Precise microscopy analyses on the cross section of the PEO coating and ZnWO 4 nanostructures confirmed that the precursors initially precipitated in the PEO coating and its surface during plasma discharge process are responsible for the nucleation and subsequent growth of metal tungstate nanostructures by thermal annealing. The method developed in this work represents a general strategy toward the rational synthesis of metal oxide nanostructures and the formation mechanism of metal tungstate nanostructures fabricated by

Synthesis of Binary Magnesium-Transition Metal Oxides via Inverse Coprecipitation

Science.gov (United States)

Yagi, Shunsuke; Ichikawa, Yuya; Yamada, Ikuya; Doi, Takayuki; Ichitsubo, Tetsu; Matsubara, Eiichiro

2013-02-01

Synthesis of binary magnesium-transition metal oxides, MgM2O4 (M: Cr, Mn, Fe, Co) and MgNiO2, was performed by calcination at relatively low temperatures of 500 and 750 °C for 24 h through inverse coprecipitation of carbonate hydroxide precursors. The important roles of the precipitation agent, sodium carbonate, were clarified by considering equilibria in an aqueous solution. The structure parameters of the obtained binary magnesium-transition metal oxide powders, specifically the occupancy of atomic sites, were evaluated from synchrotron X-ray diffraction (XRD) profiles by Rietveld refinement in addition to the magnetic properties at room temperature. The present work provides general guidelines for low-cost and high-volume synthesis of complex oxides, which are easily decomposed at high temperatures.

Review of Fabrication Methods, Physical Properties, and Applications of Nanostructured Copper Oxides Formed via Electrochemical Oxidation

Directory of Open Access Journals (Sweden)

Wojciech J. Stepniowski

2018-05-01

Full Text Available Typically, anodic oxidation of metals results in the formation of hexagonally arranged nanoporous or nanotubular oxide, with a specific oxidation state of the transition metal. Recently, the majority of transition metals have been anodized; however, the formation of copper oxides by electrochemical oxidation is yet unexplored and offers numerous, unique properties and applications. Nanowires formed by copper electrochemical oxidation are crystalline and composed of cuprous (CuO or cupric oxide (Cu2O, bringing varied physical and chemical properties to the nanostructured morphology and different band gaps: 1.44 and 2.22 eV, respectively. According to its Pourbaix (potential-pH diagram, the passivity of copper occurs at ambient and alkaline pH. In order to grow oxide nanostructures on copper, alkaline electrolytes like NaOH and KOH are used. To date, no systemic study has yet been reported on the influence of the operating conditions, such as the type of electrolyte, its temperature, and applied potential, on the morphology of the grown nanostructures. However, the numerous reports gathered in this paper will provide a certain view on the matter. After passivation, the formed nanostructures can be also post-treated. Post-treatments employ calcinations or chemical reactions, including the chemical reduction of the grown oxides. Nanostructures made of CuO or Cu2O have a broad range of potential applications. On one hand, with the use of surface morphology, the wetting contact angle is tuned. On the other hand, the chemical composition (pure Cu2O and high surface area make such materials attractive for renewable energy harvesting, including water splitting. While compared to other fabrication techniques, self-organized anodization is a facile, easy to scale-up, time-efficient approach, providing high-aspect ratio one-dimensional (1D nanostructures. Despite these advantages, there are still numerous challenges that have to be faced, including the

Introducing Barium in Transition Metal Oxide Frameworks: Impact upon Superconductivity, Magnetism, Multiferroism and Oxygen Diffusion and Storage.

Science.gov (United States)

Raveau, Bernard

2017-06-01

The role of barium in the structural chemistry of some transition metal oxides of the series "Cu, Mn, Fe,Co" is reviewed, based on its size effect and its particular chemical bonding. Its impact upon various properties, superconductivity, magnetism, multiferroism, oxygen storage is emphasized. © 2017 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Mesoporous Transition Metal Oxides for Supercapacitors

OpenAIRE

Wang, Yan; Guo, Jin; Wang, Tingfeng; Shao, Junfeng; Wang, Dong; Yang, Ying-Wei

2015-01-01

Recently, transition metal oxides, such as ruthenium oxide (RuO2), manganese dioxide (MnO2), nickel oxides (NiO) and cobalt oxide (Co3O4), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are result...

Controlling magnetism of MoS2 sheets by embedding transition-metal atoms and applying strain.

Science.gov (United States)

Zhou, Yungang; Su, Qiulei; Wang, Zhiguo; Deng, Huiqiu; Zu, Xiaotao

2013-11-14

Prompted by recent experimental achievement of transition metal (TM) atoms substituted in MoS2 nanostructures during growth or saturating existing vacancies (Sun et al., ACS Nano, 2013, 7, 3506; Deepak et al., J. Am. Chem. Soc., 2007, 129, 12549), we explored, via density functional theory, the magnetic properties of a series of 3d TM atoms substituted in a MoS2 sheet, and found that Mn, Fe, Co, Ni, Cu and Zn substitutions can induce magnetism in the MoS2 sheet. The localizing unpaired 3d electrons of TM atoms respond to the introduction of a magnetic moment. Depending on the species of TM atoms, the substituted MoS2 sheet can be a metal, semiconductor or half-metal. Remarkably, the applied elastic strain can be used to control the strength of the spin-splitting of TM-3d orbitals, leading to an effective manipulation of the magnetism of the TM-substituted MoS2 sheet. We found that the magnetic moment of the Mn- and Fe-substituted MoS2 sheets can monotonously increase with the increase of tensile strain, while the magnetic moment of Co-, Ni-, Cu- and Zn-substituted MoS2 sheets initially increases and then decreases with the increase of tensile strain. An instructive mechanism was proposed to qualitatively explain the variation of magnetism with elastic strain. The finding of the magnetoelastic effect here is technologically important for the fabrication of strain-driven spin devices on MoS2 nanostructures, which allows us to go beyond the current scope limited to the spin devices within graphene and BN-based nanostructures.

Electrochemical synthesis of magnetic nanostructures using anodic aluminum oxide templates

Science.gov (United States)

Gong, Jie

In this dissertation, template electrodeposition was employed to fabricate high quality magnetic nanostructures suited for the reliable investigation of novel spintronics phenomena such as CIMS, BMR, and CPP-GMR. Several critical aspects/steps relating to the synthesis process were investigated in this work. In order to obtain high quality magnetic nanostructures, free-standing and Si-supported anodic aluminum oxide templates with closely controlled pore diameters, lengths, as well as constriction sizes, were synthesized by anodization, followed by appropriate post-processing. The pore opening size on the barrier layer can be controlled down to 5 nm by ion beam etching. After optimization of the compositional, structural, and magnetic properties of homogeneous FeCoNiCu layers electrodeposited under different conditions, the pulsed deposition process of FeCoNI/Cu multilayers on n-Si was studied. The influence of Cu deposition potential and Fe2+ concentration on microstructure, chemical and electrochemical properties, magnetic properties, and hence magnetotransport properties were assessed. The dissolution of the FM layer during potential transition was minimized in order to control interface sharpness. Combined with the systematic sublayer thickness and FM layer composition optimization, unprecedented GMR sensitivity of 0.11%/Oe at 5-15 Oe was obtained. Growth of multilayer nanowires was performed, and contact to a single wire was attempted using an electrochemical technique. We succeeded in addressing a small number of nanowires and measured a CPP-GMR of 17%. Template electrodeposition thus provides a promising way to repeatably fabricate prototypes for spin dependent transport studies.

Metal nanostructures for non-enzymatic glucose sensing

International Nuclear Information System (INIS)

Tee, Si Yin; Teng, Choon Peng; Ye, Enyi

2017-01-01

This review covers the recent development of metal nanostructures in electrochemical non-enzymatic glucose sensing. It highlights a variety of nanostructured materials including noble metals, other transition metals, bimetallic systems, and their hybrid with carbon-based nanomaterials. Particularly, attention is devoted to numerous approaches that have been implemented for improving the sensors performance by tailoring size, shape, composition, effective surface area, adsorption capability and electron-transfer properties. The correlation of the metal nanostructures to the glucose sensing performance is addressed with respect to the linear concentration range, sensitivity and detection limit. In overall, this review provides important clues from the recent scientific achievements of glucose sensor nanomaterials which will be essentially useful in designing better and more effective electrocatalysts for future electrochemical sensing industry. - Highlights: • Overview of recent development of metal nanostructures in electrochemical non-enzymatic glucose sensing. • Special attention is focussed on noble metals, other transition metals, bimetallic systems, and their hybrid with carbon-based nanomaterials. • Merits and limitations of various metal nanostructures in electrochemical non-enzymatic glucose sensing. • Strategies to improve the glucose sensing performance of metal nanostructures as electrocatalysts.

Transition metal nuclear magnetic resonance

International Nuclear Information System (INIS)

Pregosin, P.S.

1991-01-01

Transition metal NMR spectroscopy has progressed enormously in recent years. New methods, and specifically solid-state methods and new pulse sequences, have allowed access to data from nuclei with relatively low receptivities with the result that chemists have begun to consider old and new problems, previously unapproachable. Moreover, theory, computational science in particular, now permits the calculation of not just 13 C, 15 N and other light nuclei chemical shifts, but heavy main-group element and transition metals as well. These two points, combined with increasing access to high field pulsed spectrometer has produced a wealth of new data on the NMR transition metals. A new series of articles concerned with measuring, understanding and using the nuclear magnetic resonance spectra of the metals of Group 3-12 is presented. (author)

Nanomorphology Effects in Semiconductors with Native Ferromagnetism: Hierarchical Europium (II) Oxide Tubes Prepared via a Topotactic Nanostructure Transition.

Science.gov (United States)

Trepka, Bastian; Erler, Philipp; Selzer, Severin; Kollek, Tom; Boldt, Klaus; Fonin, Mikhail; Nowak, Ulrich; Wolf, Daniel; Lubk, Axel; Polarz, Sebastian

2018-01-01

Semiconductors with native ferromagnetism barely exist and defined nanostructures are almost unknown. This lack impedes the exploration of a new class of materials characterized by a direct combination of effects on the electronic system caused by quantum confinement effects with magnetism. A good example is EuO for which currently no reliable routes for nanoparticle synthesis can be established. Bottom-up approaches applicable to other oxides fail because of the labile oxidation state +II. Instead of targeting a direct synthesis, the two steps-"structure control" and "chemical transformation"-are separated. The generation of a transitional, hybrid nanophase is followed by its conversion into EuO under full conservation of all morphological features. Hierarchical EuO materials are now accessible in the shape of oriented nanodisks stacked to tubular particles. Magnetically, the coupling of either vortex or onion states has been found. An unexpected temperature dependence is governed by thermally activated transitions between these states. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetism in 3d transition metal doped SnO

KAUST Repository

Albar, Arwa

2016-09-12

Using first principles calculations, we investigate the structural and electronic properties of 3d transition metal doped SnO. We examine the stability of different doping sites using formation energy calculations. The magnetic behavior of the dopant atoms is found to be complex because of interplay between strong structural relaxation, spin-lattice coupling, and crystal field splitting. The interaction between dopant atoms is analyzed as a function of their separation, showing that clustering typically counteracts spin polarization. An exception is found for V doping, which thus turns out to be a promising candidate for realizing a magnetic p-type oxide.

Generalized Synthesis of EAs [E = Fe, Co, Mn, Cr] Nanostructures and Investigating Their Morphology Evolution

Directory of Open Access Journals (Sweden)

P. Desai

2015-01-01

Full Text Available This paper illustrates a novel route for the synthesis of nanostructured transition metal arsenides including those of FeAs, CoAs, MnAs, and CrAs through a generalized protocol. The key feature of the method is the use of one-step hot-injection and the clever use of a combination of precursors which are low-melting and highly reactive such as metal carbonyls and triphenylarsine in a solventless setup. This method also facilitates the formation of one-dimensional nanostructures as we move across the periodic table from CrAs to CoAs. The chemical basis of this reaction is simple redox chemistry between the transition metals, wherein the transition metal is oxidized from elemental state (E0 to E3+in lieu of reduction of As3+ to As3−. While the thermodynamic analysis reveals that all these conversions are spontaneous, it is the kinetics of the process that influences morphology of the product nanostructures, which varies from extremely small nanoparticles to nanorods. Transition metal pnictides show interesting magnetic properties and these nanostructures can serve as model systems for the exploration of their intricate magnetism as well as their applications and can also function as starting materials for the arsenide based nanosuperconductors.

Preparation of the Nanostructured Radioisotope Metallic Oxide by Neutron Irradiation for Use as Radiotracers

Directory of Open Access Journals (Sweden)

Sang-Ei Seo

2017-10-01

Full Text Available Metallic oxides manganese dioxide (MnO2, samarium oxide (Sm2O3, and dysprosium oxide (Dy2O3 with nanorod-like structures were synthesized by the hydrothermal synthesis method, respectively. Subsequently, the nanostructured radioisotopes MnO2 with Mn-56, Sm2O3 with Sm-153, and Dy2O3 with Dy-165 were prepared by neutron irradiation from the HANARO research reactor, respectively. The three different elements, Mn, Sm, and Dy, were selected as radiotracers because these elements can be easily gamma-activated from neutrons (activation limits: 1 picogram (Dy, 1–10 picogram (Mn, 10–100 picogram (Sm. Furthermore, the synthesized radioisotopes can be used as radiotracers in Prompt Gamma Neutron Activation Analysis as the rare earth metals Dy and Sm were not present in the Korean environment. The successful synthesis of the radioisotope metallic oxides was confirmed by Transmission Electron Microscopy (TEM, Energy Dispersive X-ray Spectrometry (EDS, X-ray Diffraction (XRD analysis, and gamma spectroscopy analysis. The synthesized nanostructured radioisotope metallic oxides may be used as radiotracers in scientific, environmental, engineering, and industrial fields.

General Synthesis of Transition-Metal Oxide Hollow Nanospheres/Nitrogen-Doped Graphene Hybrids by Metal-Ammine Complex Chemistry for High-Performance Lithium-Ion Batteries.

Science.gov (United States)

Chen, Jiayuan; Wu, Xiaofeng; Gong, Yan; Wang, Pengfei; Li, Wenhui; Mo, Shengpeng; Peng, Shengpan; Tan, Qiangqiang; Chen, Yunfa

2018-02-09

We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co 3 O 4 , NiO, CuO-Cu 2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co 2+ , Ni 2+ , Cu 2+ , or Zn 2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH 3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co 2+ , Ni 2+ , Cu 2+ , and Zn 2+ ions, and no hollow structures formed for weak and/or noncomplex Mn 2+ and Fe 3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co 3 O 4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Topotactic reduction yielding black titanium oxide nanostructures as metallic electronic conductors.

Science.gov (United States)

Tominaka, Satoshi

2012-10-01

Detailed analyses of reduced, single crystal, rutile-type TiO(2) via high-resolution transmission electron microscopy (TEM) are reported which reveal that the reduction proceeds topotactically via interstitial diffusion of Ti ions at low temperature, around 350 °C. This important finding encouraged the production of various nanostructured reduced titanium oxides from TiO(2) precursors with morphology retention, and in the process, the synthesis of black titanium oxide nanorods using TiO(2) nanorods was demonstrated. Interestingly, as opposed to the semiconductive behavior of Ti(2)O(3) synthesized at high temperature, topotactically synthesized Ti(2)O(3) exhibits metallic electrical resistance, and the value at room temperature is quite low (topotactically synthesized Ti(2)O(3). This work shows that topotactically reduced titanium oxides can have fascinating properties as well as nanostructures.

Tuning the magnetic properties of deposited transition metal clusters by decoration

Energy Technology Data Exchange (ETDEWEB)

Minar, Jan; Bornemann, S.; Ebert, H. [Dept. Chemie, LMU, Butenandtstr. 5-13, 81377 Muenchen (Germany); Staunton, J.B. [Department of Physics, University of Warwick (United Kingdom); Rusponi, S.; Brunne, H. [EPF Lausanne (Switzerland)

2008-07-01

Using the fully relativistic version of the KKR-method for electronic structure calculations within local spin density functional theory (LSDA) the magnetic properties of Fe, Co and Ni clusters deposited on the Pt(111) surface have been investigated. Of central interest are the role of spin-orbit coupling as it influences the spontaneous formation and orientation of magnetic moments and gives rise amongst others to the occurrence of orbital magnetic moments, the magnetic anisotropy energy (MAE) and magnetic circular dichroism in X-ray absorption (XMCD). Our systematic investigations of different clusters and nanostructures aim to reveal the mutual relationship among their spin-orbit induced properties. In addition they show how their various magnetic properties depend on the structural properties and chemical composition of the studied system. For large two-dimensional clusters we focussed especially on the dependency of the MAE on decoration with another transition metal. Our results are in qualitative agreement with recent experimental findings. We resolved the MAE contributions for inequivalent cluster atoms and will discuss the effect of the induced MAE within the Pt substrate.

Study of transition metal oxides by photoelectron spectroscopy

International Nuclear Information System (INIS)

Rao, C.N.R.; Sarma, D.D.; Vasudevan, S.; Hegde, M.S.

1979-01-01

Systematics in the X-ray photoelectron spectra (X.p.e.s.) of Ti, V, Cr, Mn and Nb oxides with the metal ion in different oxidation states as well as of related series of mono-, sesqui- and di-oxides of the first row of transition metals have been investigated in detail. Core level binding energies, spin-orbit splittings and exchange splittings are found to exhibit interesting variations with the oxidation state of the metal or the nuclear charge. The 3d binding energies of the monoxides show a proportionality to Goodenough's (R - RC). Other aspects of interest in the study are the satellite structure and final state effects in the X.p.e.s. of the oxides, and identification of different valence states in oxides of the general formulae Mn02n-1 and M304. The nature of changes in the 3d bands of oxides undergoing metal-insulator transitions is also indicated. (author)

Spectroscopic study of native defects in the semiconductor to metal phase transition in V2O5 nanostructure

Science.gov (United States)

Basu, Raktima; Dhara, Sandip

2018-04-01

Vanadium is a transition metal with multiple oxidation states and V2O5 is the most stable form among them. Besides catalysis, chemical sensing, and photo-chromatic applications, V2O5 is also reported to exhibit a semiconductor to metal transition (SMT) at a temperature range of 530-560 K. Even though there are debates in using the term "SMT" for V2O5, the metallic behavior above the transition temperature and its origin are of great interest in the scientific community. In this study, V2O5 nanostructures were deposited on a SiO2/Si substrate by the vapour transport method using Au as a catalyst. Temperature dependent electrical measurement confirms the SMT in V2O5 without any structural change. Temperature dependent photoluminescence analysis proves the appearance of oxygen vacancy related peaks due to reduction of V2O5 above the transition temperature, as also inferred from temperature dependent Raman spectroscopic studies. The newly evolved defect levels in the V2O5 electronic structure with increasing temperature are also understood from the downward shift of the bottom most split-off conduction bands due to breakdown of pdπ bonds leading to metallic behavior in V2O5 above the transition temperature.

Mixed valence transition metal 2D-oxides: Comparison between delafossite and crednerite compounds

Science.gov (United States)

Martin, Christine; Poienar, Maria

2017-08-01

Transition metal oxides offer large opportunities to study relationships between structures and properties. Indeed these compounds crystallize in numerous frameworks corresponding to different dimensionalities and, accordingly, show a huge variety of properties (as high Tc superconductivity, colossal magnetoresistivity, multiferroicity..). The control of the oxidation state of the transition metal, via the monitoring of the oxygen content, is of prime importance to understand and optimize the properties, due to the strong coupling that exists between the lattice and the charges and spins of the transition metals. In this large playground for chemists, we reinvestigated several 2D-compounds derived from delafossite structure. Considering this paper as a very short review, we report here the results obtained on CuMO2 compounds (with M = Cr, Mn or Mn+Cu) by using a combination of techniques, as X-ray, neutrons and/or electrons diffraction on poly-crystals for structural characterisations that are correlated with electrical and/or magnetic properties. The complementarity of studies is also addressed by the synthesis and characterization of single crystals in addition to poly-crystals. Moreover the comparison of the structures of similar Cr and Mn based oxides highlights the crucial role of the Jahn-Teller effect of trivalent manganese to lift the degeneracy, which is responsible of the magnetic frustration in CuCrO2.

Preparation and characterization of flexible asymmetric supercapacitors based on transition-metal-oxide nanowire/single-walled carbon nanotube hybrid thin-film electrodes.

Science.gov (United States)

Chen, Po-Chiang; Shen, Guozhen; Shi, Yi; Chen, Haitian; Zhou, Chongwu

2010-08-24

In the work described in this paper, we have successfully fabricated flexible asymmetric supercapacitors (ASCs) based on transition-metal-oxide nanowire/single-walled carbon nanotube (SWNT) hybrid thin-film electrodes. These hybrid nanostructured films, with advantages of mechanical flexibility, uniform layered structures, and mesoporous surface morphology, were produced by using a filtration method. Here, manganese dioxide nanowire/SWNT hybrid films worked as the positive electrode, and indium oxide nanowire/SWNT hybrid films served as the negative electrode in a designed ASC. In our design, charges can be stored not only via electrochemical double-layer capacitance from SWNT films but also through a reversible faradic process from transition-metal-oxide nanowires. In addition, to obtain stable electrochemical behavior during charging/discharging cycles in a 2 V potential window, the mass balance between two electrodes has been optimized. Our optimized hybrid nanostructured ASCs exhibited a superior device performance with specific capacitance of 184 F/g, energy density of 25.5 Wh/kg, and columbic efficiency of approximately 90%. In addition, our ASCs exhibited a power density of 50.3 kW/kg, which is 10-fold higher than obtained in early reported ASC work. The high-performance hybrid nanostructured ASCs can find applications in conformal electrics, portable electronics, and electrical vehicles.

Impurities in Antiferromagnetic Transition-Metal Oxides - Symmetry and Optical Transitions

Science.gov (United States)

Petersen, John Emil, III

considered. For example, simple rock-salt transition-metal oxides are quite different from the high temperature superconducting cuprates. A range of materials is studied here, in order to gain a greater understanding of optical transitions in highly-correlated systems. In this work, O vacancies are introduced in NiO, along with Fe impurities, to understand better the band filling in the insulating behavior observed experimentally. These results are compared with those of La2NiO4, La2CuO4, La2-xSr xNiO4, and La2-xSrxCuO4. to elucidate the mechanisms behind the symmetry breaking phenomena in the Sr doped systems. As it turns out, indeed, the x2 - y2 orbital in these materials plays a critical role in spatial charge distribution, magnetic, and spin densities which are coupled to the dopant position in the lattice. The in-depth study of electronic and optical properties of transition-metal oxides presented here provides theoretical characterization of the infamous pseudogap in the cuprates - one of the greatest mysteries of modern solid state physics. In addition, via Density Functional Perturbation Theory, the phonon coupling with charge-density wave is explored in La2-xSr xNiO4 and found to be the dominant contributing factor to the colossal dielectric constant.

Mixing of t2 g-eg orbitals in 4 d and 5 d transition metal oxides

Science.gov (United States)

Stamokostas, Georgios L.; Fiete, Gregory A.

2018-02-01

Using exact diagonalization, we study the spin-orbit coupling and interaction-induced mixing between t2 g and egd -orbital states in a cubic crystalline environment, as commonly occurs in transition metal oxides. We make a direct comparison with the widely used t2 g-only or eg-only models, depending on electronic filling. We consider all electron fillings of the d shell and compute the total magnetic moment, the spin, the occupancy of each orbital, and the effective spin-orbit coupling strength (renormalized through interaction effects) in terms of the bare interaction parameters, spin-orbit coupling, and crystal-field splitting, focusing on the parameter ranges relevant to 4 d and 5 d transition metal oxides. In various limits, we provide perturbative results consistent with our numerical calculations. We find that the t2 g-eg mixing can be large, with up to 20% occupation of orbitals that are nominally "empty," which has experimental implications for the interpretation of the branching ratio in experiments, and can impact the effective local moment Hamiltonian used to study magnetic phases and magnetic excitations in transition metal oxides. Our results can aid the theoretical interpretation of experiments on these materials, which often fall in a regime of intermediate coupling with respect to electron-electron interactions.

Ordering phenomena in transition-metal-oxide heterostructures

International Nuclear Information System (INIS)

Frano Pereira, Alex Manuel

2014-01-01

This doctoral work presents a study of ordered ground states of transition metal oxide compounds and multilayers using resonant elastic soft x-ray scattering. The technique has developed over the last decades and become especially useful when sample sizes are limited like the case of nanometer-scale films and superlattices. By scattering with photon energies on resonance with the element's electronic transitions, it is an element-specific, sensitive tool providing a combination of spectroscopic and spatial information. The thesis is divided into two central topics. The first part focuses on the investigation of perovskite-type, rare-earth nickelate heterostructures. X-rays tuned to the Ni L 3 -edge were used to unveil unprecedented diffraction evidence of long range magnetic order in LaNiO 3 -RXO 3 (RXO 3 = LaAlO 3 , DyScO 3 ) superlattices. We report on the appearance of magnetic order in such systems with a propagation vector of Q SDW = ((1)/(4),(1)/(4),l) in pseudocubic notation, similar to bulk rare earth nickelates with R ≠ La. With LaNiO 3 being paramagnetic in its bulk form, the magnetic Bragg peak is only present in superlattices where the thickness of the LaNiO 3 layers approaches the 2-dimensional limit. Besides the thickness dependence, the magnetic order was probed on samples grown on varying strain-inducing substrates. Azimuthal scans around Q SDW were done to determine the orientation of the spin spiral under these different conditions. We will explain how the reorientation of the spins can be understood by the magneto-crystalline anisotropy which is determined by the relative occupation of the Ni d-orbitals via spin-orbit coupling. First steps towards control of the spin spiral's orientation will be outlined, and along with the high remanent conductivity found in the magnetic spiral state, an outlook for metallic antiferromagnetic spintronics will be discussed. The second part of this thesis will address the observation of charge density

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

Science.gov (United States)

Wang, Xuefeng

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

First-Row-Transition Ion Metals(II-EDTA Functionalized Magnetic Nanoparticles as Catalysts for Solvent-Free Microwave-Induced Oxidation of Alcohols

Directory of Open Access Journals (Sweden)

Nuno M. R. Martins

2017-11-01

Full Text Available A series of first-row transition-metals combined with ethylenediamine tetraacetic acid (EDTA, as metal-based N,O-chelating ligands, at the surface of ferrite magnetic nanoparticles (MNPs was prepared by a co-precipitation method. Those EDTA functionalized MNPs with general formula Fe3O4@EDTA-M2+ [M = Mn2+ (1, Fe2+ (2, Co2+ (3, Ni2+ (4, Cu2+ (5 or Zn2+ (6] were characterized by FTIR (Fourier Transform Infrared spectroscopy, powder XRD (X-ray Diffraction, SEM (Scanning Electron Microscope, EDS (Energy Dispersive Spectrometer, VSM (Vibrating Sample Magnetometer and TGA (Thermal Gravity Analysis. The application of the magnetic NPs towards the microwave-assisted oxidation of several alcohol substrates in a solvent-free medium was evaluated. The influence of reaction parameters such as temperature, time, type of oxidant, and presence of organic radicals was investigated. This study demonstrates that these MNPs can act as efficient catalysts for the conversion of alcohols to the corresponding ketones or aldehydes with high selectivity and yields up to 99% after 2 h of reaction at 110 °C using t-BuOOH as oxidant. Moreover, they have the advantage of being magnetically recoverable catalysts that can be easily recycled in following runs.

Interfaces and nanostructures of oxide octahedral frameworks

Directory of Open Access Journals (Sweden)

Felip eSandiumenge

2014-08-01

Full Text Available In the past decade, the rich physics exhibited by solid interfaces combining octahedral framework structures of transition metal oxides has fascinated the materials science community. However, the behavior of these materials still elude the current understanding of classical semiconductor and metal epitaxy. The reason for that is rooted in the surprising versatility of linked coordination units to adapt to a dissimilar substrate and the strong sensitivity of correlated oxides to external perturbations. The confluence of atomic control in oxide thin film epitaxy, state of the art high spatial resolution characterization techniques, and electronic structure computations, has allowed in recent years to obtain first insights on the underlying microscopic mechanisms governing the epitaxy of these fascinating materials. Here, we shortly review these mechanisms and highlight their potential in the design of novel nanostructures with enhanced functionalities.

Near-field effects and energy transfer in hybrid metal-oxide nanostructures.

Science.gov (United States)

Herr, Ulrich; Kuerbanjiang, Balati; Benel, Cahit; Papageorgiou, Giorgos; Goncalves, Manuel; Boneberg, Johannes; Leiderer, Paul; Ziemann, Paul; Marek, Peter; Hahn, Horst

2013-01-01

One of the big challenges of the 21st century is the utilization of nanotechnology for energy technology. Nanoscale structures may provide novel functionality, which has been demonstrated most convincingly by successful applications such as dye-sensitized solar cells introduced by M. Grätzel. Applications in energy technology are based on the transfer and conversion of energy. Following the example of photosynthesis, this requires a combination of light harvesting, transfer of energy to a reaction center, and conversion to other forms of energy by charge separation and transfer. This may be achieved by utilizing hybrid nanostructures, which combine metallic and nonmetallic components. Metallic nanostructures can interact strongly with light. Plasmonic excitations of such structures can cause local enhancement of the electrical field, which has been utilized in spectroscopy for many years. On the other hand, the excited states in metallic structures decay over very short lifetimes. Longer lifetimes of excited states occur in nonmetallic nanostructures, which makes them attractive for further energy transfer before recombination or relaxation sets in. Therefore, the combination of metallic nanostructures with nonmetallic materials is of great interest. We report investigations of hybrid nanostructured model systems that consist of a combination of metallic nanoantennas (fabricated by nanosphere lithography, NSL) and oxide nanoparticles. The oxide particles were doped with rare-earth (RE) ions, which show a large shift between absorption and emission wavelengths, allowing us to investigate the energy-transfer processes in detail. The main focus is on TiO2 nanoparticles doped with Eu(3+), since the material is interesting for applications such as the generation of hydrogen by photocatalytic splitting of water molecules. We use high-resolution techniques such as confocal fluorescence microscopy for the investigation of energy-transfer processes. The experiments are

Low-angle polarized neutron and X-ray scattering from magnetic nanolayers and nanostructures

CERN Document Server

Paul, Amitesh

2017-01-01

This research monograph presents the latest results related to the characterization of low dimensional systems. Low-angle polarized neutron scattering and X-ray scattering at grazing incidence are used as the two main techniques to explore various physical phenomena of these systems. Special focus is put on systems like thin film transition metal and rare-earth layers, oxide heterostructures, hybrid systems, self-assembled nanostructures and self-diffusion.  Readers will gain in-depth knowledge about the usage of specular scattering and off-specular scattering techniques. Investigation of in-plane and out-of-plane structures and magnetism with vector magnetometric information is illustrated comprehensively. The book caters to a wide audience working in the field of nano-dimensional magnetic systems and the neutron and X-ray reflectometry community in particular.

Ordering phenomena in transition-metal-oxide heterostructures

Energy Technology Data Exchange (ETDEWEB)

Frano Pereira, Alex Manuel

2014-01-27

This doctoral work presents a study of ordered ground states of transition metal oxide compounds and multilayers using resonant elastic soft x-ray scattering. The technique has developed over the last decades and become especially useful when sample sizes are limited like the case of nanometer-scale films and superlattices. By scattering with photon energies on resonance with the element's electronic transitions, it is an element-specific, sensitive tool providing a combination of spectroscopic and spatial information. The thesis is divided into two central topics. The first part focuses on the investigation of perovskite-type, rare-earth nickelate heterostructures. X-rays tuned to the Ni L{sub 3}-edge were used to unveil unprecedented diffraction evidence of long range magnetic order in LaNiO{sub 3}-RXO{sub 3} (RXO{sub 3} = LaAlO{sub 3}, DyScO{sub 3}) superlattices. We report on the appearance of magnetic order in such systems with a propagation vector of Q{sub SDW} = ((1)/(4),(1)/(4),l) in pseudocubic notation, similar to bulk rare earth nickelates with R ≠ La. With LaNiO{sub 3} being paramagnetic in its bulk form, the magnetic Bragg peak is only present in superlattices where the thickness of the LaNiO{sub 3} layers approaches the 2-dimensional limit. Besides the thickness dependence, the magnetic order was probed on samples grown on varying strain-inducing substrates. Azimuthal scans around Q{sub SDW} were done to determine the orientation of the spin spiral under these different conditions. We will explain how the reorientation of the spins can be understood by the magneto-crystalline anisotropy which is determined by the relative occupation of the Ni d-orbitals via spin-orbit coupling. First steps towards control of the spin spiral's orientation will be outlined, and along with the high remanent conductivity found in the magnetic spiral state, an outlook for metallic antiferromagnetic spintronics will be discussed. The second part of this thesis

Preparation and characterization of several transition metal oxides

International Nuclear Information System (INIS)

Wold, A.; Dwight, K.

1989-01-01

The structure-property relationships of several conducting transition metal oxides, as well as their preparative methods, are presented in this paper. The importance of preparing homogeneous phases with precisely known stoichiometry is emphasized. A comparison is also made of the various techniques used to prepare both polycrystalline and single crystal samples. For transition metal oxides, the metallic properties are discussed either in terms of metal-metal distances which are short enough to result in metallic behavior, or in terms of the formation of a π* conduction band resulting from covalent metal-oxygen interactions. Metallic behavior is observed when the conduction bands are populated with either electrons or holes. The concentration of these carriers can be affected by either cation or anion substitutions. The discussion in this presentation will be limited to the elements Re, Ti, V, Cr, Mo, and Cu

Electrochromism in transition metal oxides

International Nuclear Information System (INIS)

Estrada, W.

1993-01-01

Electrochromism is discussed for transition metal oxides. Particularly tungsten oxide and nickel oxide are reviewed, in order to put forth the different aspects of the field. Since this phenomena has been reviewed by several authors, it is not tried to be comprehensive but rather pedagogical. The basic requirements for a material -in both non-emissive displays and energy efficiency applications- to be electrochromic, a general view of electrochromic mechanism, anodic and cathodic electrochromic materials, and current problems for a electrochromic theory are presented. (author) 45 refs., 8 figs

Transition Metal Dopants Essential for Producing Ferromagnetism in Metal Oxide Nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Johnson, Lydia; Thurber, Aaron P.; Anghel, Josh; Sabetian, Maryam; Engelhard, Mark H.; Tenne, D.; Hanna, Charles; Punnoose, Alex

2010-08-13

Recent claims that ferromagnetism can be produced in nanoparticles of metal oxides without the presence of transition metal dopants has been refuted in this work by investigating 62 high quality well-characterized nanoparticle samples of both undoped and Fe doped (0-10% Fe) ZnO. The undoped ZnO nanoparticles showed zero or negligible magnetization, without any dependence on the nanoparticle size. However, chemically synthesized Zn₁₋xFexO nanoparticles showed clear ferromagnetism, varying systematically with Fe concentration. Furthermore, the magnetic properties of Zn₁₋xFexO nanoparticles showed strong dependence on the reaction media used to prepare the samples. The zeta potentials of the Zn₁₋xFexO nanoparticles prepared using different reaction media were significantly different, indicating strong differences in the surface structure. Electron paramagnetic resonance studies clearly showed that the difference in the ferromagnetic properties of Zn₁₋xFexO nanoparticles with different surface structures originate from differences in the fraction of the doped Fe³⁺ ions that are coupled ferromagnetically.

Manganese Nanostructures and Magnetism

Science.gov (United States)

Simov, Kirie Rangelov

The primary goal of this study is to incorporate adatoms with large magnetic moment, such as Mn, into two technologically significant group IV semiconductor (SC) matrices, e.g. Si and Ge. For the first time in the world, we experimentally demonstrate Mn doping by embedding nanostructured thin layers, i.e. delta-doping. The growth is observed by in-situ scanning tunneling microscopy (STM), which combines topographic and electronic information in a single image. We investigate the initial stages of Mn monolayer growth on a Si(100)(2x1) surface reconstruction, develop methods for classification of nanostructure types for a range of surface defect concentrations (1.0 to 18.2%), and subsequently encapsulate the thin Mn layer in a SC matrix. These experiments are instrumental in generating a surface processing diagram for self-assembly of monoatomic Mn-wires. The role of surface vacancies has also been studied by kinetic Monte Carlo modeling and the experimental observations are compared with the simulation results, leading to the conclusion that Si(100)(2x1) vacancies serve as nucleation centers in the Mn-Si system. Oxide formation, which happens readily in air, is detrimental to ferromagnetism and lessens the magnetic properties of the nanostructures. Therefore, the protective SC cap, composed of either Si or Ge, serves a dual purpose: it is both the embedding matrix for the Mn nanostructured thin film and a protective agent for oxidation. STM observations of partially deposited caps ensure that the nanostructures remain intact during growth. Lastly, the relationship between magnetism and nanostructure types is established by an in-depth study using x-ray magnetic circular dichroism (XMCD). This sensitive method detects signals even at coverages less than one atomic layer of Mn. XMCD is capable of discerning which chemical compounds contribute to the magnetic moment of the system, and provides a ratio between the orbital and spin contributions. Depending on the amount

Local Symmetry and Domain Patterns: Ordering Phenomena in Transition-Metal Oxides

OpenAIRE

Buchholz, Marcel

2013-01-01

Transition-metal oxides (TMOs) show rich phase diagrams with various magnetic and electronic phases that arise from the complex interplay between spin, charge, orbital, and lattice degrees of freedom. The most prominent class of materials, which has attracted a lot of attention in the last decades, are probably high-temperature superconductors (HTS), in which the resitivity drops to zero below a critical temperature. Further examples are different kind of complex ordering phenomena, for examp...

A Systematic Transport and Thermodynamic Study of Heavy Transition Metal Oxides with Hexagonal Structure

Science.gov (United States)

Butrouna, Kamal

There is no apparent, dominant interaction in heavy transition metal oxides (TMO), especially in 5d-TMO, where all relevant interactions are of comparable energy scales, and therefore strongly compete. In particular, the spin-orbit interaction (SOI) strongly competes with the electron-lattice and on-site Coulomb interaction (U). Therefore, any tool that allows one to tune the relative strengths of SOI and U is expected to offer an opportunity for the discovery and study of novel materials. BaIrO3 is a magnetic insulator driven by SOI, whereas the isostructural BaRuO3 is a paramagnetic metal. The contrasting ground states have been shown to result from the critical role of SOI in the iridate. This dissertation thoroughly examines a wide array of newly observed novel phenomena induced by adjusting the relative strengths of SOI and U via a systematic chemical substitution of the Ru4+(4d 4) ions for Ir4+(5d5) ions in BaIrO3, i.e., in high quality single crystals of BaIr1--x RuxO3(0.0 ≤ x ≤ 1.0). Our investigation of structural, magnetic, transport and thermal properties reveals that Ru substitution directly rebalances the competing energies so profoundly that it generates a rich phase diagram for BaIr 1--xRuxO 3 featuring two major effects: (1) Light Ru doping (0 ≤ x ≤ 0.15) prompts a simultaneous and precipitous drop in both the magnetic ordering temperature TC and the electrical resistivity, which exhibits metal-insulator transition at around TC. (2) Heavier Ru doping (0.41 ≤ x ≤ 0.82) induces a robust metallic and spin frustration state. For comparison and contrast, we also substituted Rh4+(4d 5) ions for Ir4+(5d5) ions in BaIrO3, i.e. in BaIr1--xRhxO 3(0.0 ≤ x ≤ 0.1), where Rh only reduces the SOI, but without altering the band filling. Hence, this system remains tuned at the Mott instability and is very susceptible to disorder scattering which gives rise to Anderson localization. KEYWORDS: spin-orbit interaction, heavy transition metal oxides

Magnetic engineering in 3d transition metals on phosphorene by strain

International Nuclear Information System (INIS)

Cai, Xiaolin; Niu, Chunyao; Wang, Jianjun; Yu, Weiyang; Ren, XiaoYan; Zhu, Zhili

2017-01-01

Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

Magnetic engineering in 3d transition metals on phosphorene by strain

Energy Technology Data Exchange (ETDEWEB)

Cai, Xiaolin [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Niu, Chunyao, E-mail: niuchunyao@zzu.edu.cn [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); Wang, Jianjun [College of Science, Zhongyuan University of Technology, Zhengzhou 450007 (China); Yu, Weiyang [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China); School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo, 454000 (China); Ren, XiaoYan; Zhu, Zhili [International Laboratory for Quantum Functional Materials of Henan and School of Physics and Engineering, Zhengzhou University, Zhengzhou, 450001 (China)

2017-04-11

Using first-principles density functional theory (DFT) calculations, we systematically investigate the strain effects on the adsorption energies, magnetic ordering and electronic properties of 3d transition metal (TM) atoms (from Sc to Co) adsorbed on phosphorene (P). We find that the adsorption energy of TM can be enhanced by compressive strain whereas weakened by tensile strain. Our results show that strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. Importantly, the transitions from antiferromagnetic (AFM) state to ferromagnetic (FM) state or to another different AFM ordering can be induced by strain effect. In addition, we observe the semiconductor to metal or half-metal transitions in some TM@P systems by applying strain. Our findings shed a new light on precisely engineering the magnetic properties and electronic properties of the TM@P systems, which will have great potential applications in spin electronics and other related fields. - Highlights: • The adsorption of TM atoms on phosphorene can be enhanced by compressive strain whereas weakened by tensile strain. • Strain plays a decisive role in the magnetic moments as well as the magnetic coupling states of TM adatoms. • Applying strain can induce the semiconductor to metal or half-metal transitions in some TM@P systems.

Electroforming and Switching in Oxides of Transition Metals: The Role of Metal Insulator Transition in the Switching Mechanism

Science.gov (United States)

Chudnovskii, F. A.; Odynets, L. L.; Pergament, A. L.; Stefanovich, G. B.

1996-02-01

Electroforming and switching effects in sandwich structures based on anodic films of transition metal oxides (V, Nb, Ti, Fe, Ta, W, Zr, Hf, Mo) have been studied. After being electroformed, some materials exhibited current-controlled negative resistance with S-shapedV-Icharacteristics. For V, Fe, Ti, and Nb oxides, the temperature dependences of the threshold voltage have been measured. As the temperature increased,Vthdecreased to zero at a critical temperatureT0, which depended on the film material. Comparison of theT0values with the temperatures of metal-insulator phase transition for some compounds (Tt= 120 K for Fe3O4, 340 K for VO2, ∼500 K for Ti2O3, and 1070 K for NbO2) showed that switching was related to the transition in the applied electric field. Channels consisting of the above-mentioned lower oxides were formed in the initial anodic films during the electroforming. The possibility of formation of these oxides with a metal-insulator transition was confirmed by thermodynamic calculations.

Preparation and properties of novel magnetic composite nanostructures: Arrays of nanowires in porous membranes

International Nuclear Information System (INIS)

Vazquez, M.; Hernandez-Velez, M.; Asenjo, A.; Navas, D.; Pirota, K.; Prida, V.; Sanchez, O.; Baldonedo, J.L.

2006-01-01

In the present work, we introduce our latest achievements in the development of novel highly ordered composite magnetic nanostructures employing anodized nanoporous membranes as precursor templates where long-range hexagonal symmetry is induced by self-assembling during anodization process. Subsequent processing as electroplating, sputtering or pressing are employed to prepare arrays of metallic, semiconductor or polymeric nanowires embedded in oxide or metallic membranes. Particular attention is paid to recent results on controlling the magnetic anisotropy in arrays of metallic nanowires, particularly Co, and nanohole arrays in Ni membranes

Electronic and Magnetic Properties of Transition-Metal Oxide Nanocomposites: A Tight-Binding Modeling at Mesoscale

Science.gov (United States)

Tai, Yuan-Yen; Zhu, Jian-Xin

Transition metal oxides (TMOs) exhibit many emergent phenomena ranging from high-temperature superconductivity and giant magnetoresistance to magnetism and ferroelectricity. In addition, when TMOs are interfaced with each other, new functionalities can arise, which are absent in individual components. In this talk, I will present an overview on our recent efforts in theoretical understanding of the electronic and magnetic properties TMO nanocomposites. In particular, I will introduce our recently developed tight-binding modeling of these properties arising from the interplay of competing interactions at the interfaces of planar and pillar nanocomposites. Our theoretical tool package will provide a unique capability to address the emergent phenomena in TMO nanocomposites and their mesoscale response to such effects like strain and microstructures at the interfaces, and ultimately help establish design principles of new multifunctionality with TMOs. This work was carried out under the auspices of the National Nuclear Security Administration of the U.S. Department of Energy at LANL under Contract No. DE-AC52-06NA25396, and was supported by the LANL LDRD Program.

Synthesis and characterization of nanostructured transition metal oxides for energy storage devices

Science.gov (United States)

Kim, Jong Woung

Finding a promising material and constructing a new method to have both high energy and power are key issues for future energy storage systems. This dissertation addresses three different materials systems to resolve those issues. Pseudocapacitive materials such as RuO2 and MnO2 display high capacitance but Nb2O5, displays a different charge storage mechanism, one highly dependent on its crystal phase rather than its surface area. Various sol-gel techniques were used to synthesize the different phases of Nb2O5 and electrochemical testing was used to study their charge storage with some phases displaying comparable charge storage to MnO2. To overcome the electrical limitations of using an insulating material, the core-shell structure (Nb2O 5/C) was also examined and the method could be generalized to improve other pseudocapacitors. Besides electronic conductivity, the diffusion of the electrolyte ions through the shell material is a critical factor for fast charging/discharging in the core-shell structure. This dissertation also involves another topic, a reconfigurable electrode, that displays both high energy and power density. By constructing a reconfigurable electrode which has different electrical properties (metallic or insulating state) depending on the amount of intercalated `guest' ions into `host' material, it can be used as a battery or electrochemical capacitor material in the insulating or metallic state respectively. Metal oxide bronzes having metal-insulator transition were investigated in this study.

A Self-Templating Scheme for the Synthesis of Nanostructured Transition Metal Chalcogenide Electrodes for Capacitive Energy Storage

KAUST Repository

Xia, Chuan; Alshareef, Husam N.

2015-01-01

Due to their unique structural features including well-defined interior voids, low density, low coefficients of thermal expansion, large surface area and surface permeability, hollow micro/nanostructured transition metal sulfides with high

Hydroxylation of benzene to phenol over magnetic recyclable nanostructured CuFe mixed-oxide catalyst

CSIR Research Space (South Africa)

Makgwane, PR

2015-03-01

Full Text Available A highly active and magnetically recyclable nanostructured copper–iron oxide (CuFe) catalyst has been synthesized for hydroxylation of benzene to phenol under mild reaction conditions. The obtained catalytic results were correlated with the catalyst...

Removal of Heavy Metals from Drinking Water by Magnetic Carbon Nanostructures Prepared from Biomass

OpenAIRE

Muneeb Ur Rahman Khattak, Muhammad; Zahoor, Muhammad; Muhammad, Bakhtiar; Khan, Farhat Ali; Ullah, Riaz; AbdEI-Salam, Naser M.

2017-01-01

Heavy metals contamination of drinking water has significant adverse effects on human health due to their toxic nature. In this study a new adsorbent, magnetic graphitic nanostructures were prepared from watermelon waste. The adsorbent was characterized by different instrumental techniques (surface area analyzer, FTIR, XRD, EDX, SEM, and TG/DTA) and was used for the removal of heavy metals (As, Cr, Cu, Pb, and Zn) from water. The adsorption parameters were determined for heavy metals adsorpti...

Hard X-ray PhotoElectron Spectroscopy of transition metal oxides: Bulk compounds and device-ready metal-oxide interfaces

International Nuclear Information System (INIS)

Borgatti, F.; Torelli, P.; Panaccione, G.

2016-01-01

Highlights: • Hard X-ray PhotoElectron Spectroscopy (HAXPES) applied to buried interfaces of systems involving Transition Metal Oxides. • Enhanced contribution of the s states at high kinetic energies both for valence and core level spectra. • Sensitivity to chemical changes promoted by electric field across metal-oxide interfaces in resistive switching devices. - Abstract: Photoelectron spectroscopy is one of the most powerful tool to unravel the electronic structure of strongly correlated materials also thanks to the extremely large dynamic range in energy, coupled to high energy resolution that this form of spectroscopy covers. The kinetic energy range typically used for photoelectron experiments corresponds often to a strong surface sensitivity, and this turns out to be a disadvantage for the study of transition metal oxides, systems where structural and electronic reconstruction, different oxidation state, and electronic correlation may significantly vary at the surface. We report here selected Hard X-ray PhotoElectron Spectroscopy (HAXPES) results from transition metal oxides, and from buried interfaces, where we highlight some of the important features that such bulk sensitive technique brings in the analysis of electronic properties of the solids.

Hard X-ray PhotoElectron Spectroscopy of transition metal oxides: Bulk compounds and device-ready metal-oxide interfaces

Energy Technology Data Exchange (ETDEWEB)

Borgatti, F., E-mail: francesco.borgatti@cnr.it [Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), Consiglio Nazionale delle Ricerche (CNR), via P. Gobetti 101, Bologna I-40129 (Italy); Torelli, P.; Panaccione, G. [Istituto Officina dei Materiali (IOM)-CNR, Laboratorio TASC, Area Science Park, Trieste I-34149 (Italy)

2016-04-15

Highlights: • Hard X-ray PhotoElectron Spectroscopy (HAXPES) applied to buried interfaces of systems involving Transition Metal Oxides. • Enhanced contribution of the s states at high kinetic energies both for valence and core level spectra. • Sensitivity to chemical changes promoted by electric field across metal-oxide interfaces in resistive switching devices. - Abstract: Photoelectron spectroscopy is one of the most powerful tool to unravel the electronic structure of strongly correlated materials also thanks to the extremely large dynamic range in energy, coupled to high energy resolution that this form of spectroscopy covers. The kinetic energy range typically used for photoelectron experiments corresponds often to a strong surface sensitivity, and this turns out to be a disadvantage for the study of transition metal oxides, systems where structural and electronic reconstruction, different oxidation state, and electronic correlation may significantly vary at the surface. We report here selected Hard X-ray PhotoElectron Spectroscopy (HAXPES) results from transition metal oxides, and from buried interfaces, where we highlight some of the important features that such bulk sensitive technique brings in the analysis of electronic properties of the solids.

Electronic structure, magnetism, and exchange integrals in transition-metal oxides: Role of the spin polarization of the functional in DFT+U calculations

Science.gov (United States)

Keshavarz, Samara; Schött, Johan; Millis, Andrew J.; Kvashnin, Yaroslav O.

2018-05-01

Density functional theory augmented with Hubbard-U corrections (DFT+U ) is currently one of the most widely used methods for first-principles electronic structure modeling of insulating transition-metal oxides (TMOs). Since U is relatively large compared to bandwidths, the magnetic excitations in TMOs are expected to be well described by a Heisenberg model. However, in practice the calculated exchange parameters Ji j depend on the magnetic configuration from which they are extracted and on the functional used to compute them. In this work we investigate how the spin polarization dependence of the underlying exchange-correlation functional influences the calculated magnetic exchange constants of TMOs. We perform a systematic study of the predictions of calculations based on the local density approximation plus U (LDA+U ) and the local spin density approximation plus U (LSDA+U ) for the electronic structures, total energies, and magnetic exchange interactions Ji j extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of several transition-metal oxide materials. We report that for realistic choices of Hubbard U and Hund's J parameters, LSDA+U and LDA+U calculations result in different values of the magnetic exchange constants and band gap. The dependence of the band gap on the magnetic configuration is stronger in LDA+U than in LSDA+U and we argue that this is the main reason why the configuration dependence of Ji j is found to be systematically more pronounced in LDA+U than in LSDA+U calculations. We report a very good correspondence between the computed total energies and the parametrized Heisenberg model for LDA+U calculations, but not for LSDA+U , suggesting that LDA+U is a more appropriate method for estimating exchange interactions.

First-principles study of doping effect on the phase transition of zinc oxide with transition metal doped

International Nuclear Information System (INIS)

Wu, Liang; Hou, Tingjun; Wang, Yi; Zhao, Yanfei; Guo, Zhenyu; Li, Youyong; Lee, Shuit-Tong

2012-01-01

Highlights: ► We study the doping effect on B4, B1 structures and phase transition of ZnO. ► We calculate the phase transition barrier and phase transition path of doped ZnO. ► The transition metal doping decreases the bulk modulus and phase transition pressure. ► The magnetic properties are influenced by the phase transition process. - Abstract: Zinc oxide (ZnO) is a promising material for its wide application in solid-state devices. With the pressure raised from an ambient condition, ZnO transforms from fourfold wurtzite (B4) to sixfold coordinated rocksalt (B1) structure. Doping is an efficient approach to improve the structures and properties of materials. Here we use density-functional theory (DFT) to study doped ZnO and find that the transition pressure from B4 phase to B1 phase of ZnO always decreases with different types of transition metal (V, Cr, Mn, Fe, Co, or Ni) doped, but the phase transition path is not affected by doping. This is consistent with the available experimental results for Mn-doped ZnO and Co-doped ZnO. Doping in ZnO causes the lattice distortion, which leads to the decrease of the bulk modulus and accelerates the phase transition. Mn-doped ZnO shows the strongest magnetic moment due to its half filled d orbital. For V-doped ZnO and Cr-doped ZnO, the magnetism is enhanced by phase transition from B4 to B1. But for Mn-doped ZnO, Fe-doped ZnO, Co-doped ZnO, and Ni-doped ZnO, B1 phase shows weaker magnetic moment than B4 phase. These results can be explained by the amount of charge transferred from the doped atom to O atom. Our results provide a theoretical basis for the doping approach to change the structures and properties of ZnO.

Oxide nanostructures on a Nb surface and related systems: experiments and ab initio calculations

International Nuclear Information System (INIS)

Kuznetsov, Mikhail V; Razinkin, A S; Ivanovskii, Alexander L

2011-01-01

This review discusses the state of the art in two related research areas: the surfaces of niobium and of its related group IV-VI transition metals, and surface (primarily oxide) nanostructures that form on niobium (and group IV-VI d-metals) due to gas adsorption or impurity diffusion from the bulk. Experimental (X-ray photoelectron spectroscopy, photoelectron diffraction, scanning tunneling microscopy) and theoretical (ab initio simulation) results on d-metal surfaces are summarized and reviewed. (reviews of topical problems)

Template-directed formation of functional complex metal-oxide nanostructures by combination of sol-gel processing and spin coating

International Nuclear Information System (INIS)

Choi, Y.C.; Kim, J.; Bu, S.D.

2006-01-01

We report the template-based formation of functional complex metal-oxide nanostructures by a combination of sol-gel processing and spin coating. This method employs the spin-coating of a sol-gel solution into an anodic aluminum oxide membrane (SSAM). Various metal-oxide nanowires and nanotubes with a high aspect-ratio were prepared. The aspect-ratios of the PbO 2 nanowires and Pb(Zr 0.52 Ti 0.48 )O 3 nanowires were about 300 and 400, respectively, and their diameters were about 50 nm. The fabricated PbTiO 3 nanotubes have a relatively constant wall thickness of about 20 nm with an outer diameter of about 60 nm. The deposition time for all of the fabricated metal-oxide nanowires and nanotubes is less than 120 s, which is far shorter than those required in both the sol-gel dipping and sol-gel electrophoretic methods. These results indicate that the SSAM method can be a versatile pathway to prepare functional complex metal-oxide nanowires and nanotubes with a high aspect-ratio. The possible formation process for the one-dimensional nanostructures by SSAM is discussed

Metal-insulator transitions

Science.gov (United States)

Imada, Masatoshi; Fujimori, Atsushi; Tokura, Yoshinori

1998-10-01

Metal-insulator transitions are accompanied by huge resistivity changes, even over tens of orders of magnitude, and are widely observed in condensed-matter systems. This article presents the observations and current understanding of the metal-insulator transition with a pedagogical introduction to the subject. Especially important are the transitions driven by correlation effects associated with the electron-electron interaction. The insulating phase caused by the correlation effects is categorized as the Mott Insulator. Near the transition point the metallic state shows fluctuations and orderings in the spin, charge, and orbital degrees of freedom. The properties of these metals are frequently quite different from those of ordinary metals, as measured by transport, optical, and magnetic probes. The review first describes theoretical approaches to the unusual metallic states and to the metal-insulator transition. The Fermi-liquid theory treats the correlations that can be adiabatically connected with the noninteracting picture. Strong-coupling models that do not require Fermi-liquid behavior have also been developed. Much work has also been done on the scaling theory of the transition. A central issue for this review is the evaluation of these approaches in simple theoretical systems such as the Hubbard model and t-J models. Another key issue is strong competition among various orderings as in the interplay of spin and orbital fluctuations. Experimentally, the unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. In particular, there is revived interest in transition-metal oxides, motivated by the epoch-making findings of high-temperature superconductivity in cuprates and colossal magnetoresistance in manganites. The article reviews the rich phenomena of anomalous metallicity, taking as examples Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Ru compounds. The diverse phenomena include strong spin and

Probing of O2 vacancy defects and correlated magnetic, electrical and photoresponse properties in indium-tin oxide nanostructures by spectroscopic techniques

Science.gov (United States)

Ghosh, Shyamsundar; Dev, Bhupendra Nath

2018-05-01

Indium-tin oxide (ITO) 1D nanostructures with tunable morphologies i.e. nanorods, nanocombs and nanowires are grown on c-axis (0 0 0 1) sapphire (Al2O3) substrate in oxygen deficient atmosphere through pulsed laser deposition (PLD) technique and the effect of oxygen vacancies on optical, electrical, magnetic and photoresponse properties is investigated using spectroscopic methods. ITO nanostructures are found to be enriched with significant oxygen vacancy defects as evident from X-ray photoelectron and Raman spectroscopic analysis. Photoluminescence spectra exhibited intense mid-band blue emission at wavelength of region of 400-450 nm due to the electronic transition from conduction band maxima (CBM) to the singly ionized oxygen-vacancy (VO+) defect level within the band-gap. Interestingly, ITO nanostructures exhibited significant room-temperature ferromagnetism (RTFM) and the magnetic moment found proportional to concentration of VO+ defects which indicates VO+ defects are mainly responsible for the observed RTFM in nanostructures. ITO nanowires being enriched with more VO+ defects exhibited strongest RTFM as compared to other morphologies. Current voltage (I-V) characteristics of ITO nanostructures showed an enhancement of current under UV light as compared to dark which indicates such 1D nanostructure can be used as photovoltaic material. Hence, the study shows that there is ample opportunity to tailor the properties of ITOs through proper defect engineering's and such photosensitive ferromagnetic semiconductors might be promising for spintronic and photovoltaic applications.

Metal-core@metal oxide-shell nanomaterials for gas-sensing applications: a review

Energy Technology Data Exchange (ETDEWEB)

Mirzaei, A.; Janghorban, K.; Hashemi, B. [Shiraz University, Department of Materials Science and Engineering (Iran, Islamic Republic of); Neri, G., E-mail: gneri@unime.it [University of Messina, Department of Electronic Engineering, Chemistry and Industrial Engineering (Italy)

2015-09-15

With an ever-increasing number of applications in many advanced fields, gas sensors are becoming indispensable devices in our daily life. Among different types of gas sensors, conductometric metal oxide semiconductor (MOS) gas sensors are found to be the most appealing for advanced applications in the automotive, biomedical, environmental, and safety sectors because of the their high sensitivity, reduced size, and low cost. To improve their sensing characteristics, new metal oxide-based nanostructures have thus been proposed in recent years as sensing materials. In this review, we extensively review gas-sensing properties of core@ shell nanocomposites in which metals as the core and metal oxides as the shell structure, both of nanometer sizes, are assembled into a single metal@metal oxide core–shell. These nanostructures not only combine the properties of both noble metals and metal oxides, but also bring unique synergetic functions in comparison with single-component materials. Up-dated achievements in the synthesis and characterization of metal@metal oxide core–shell nanostructures as well as their use in MOS sensors are here reported with the main objective of providing an overview about their gas-sensing properties.

A microbial-mineralization-inspired approach for synthesis of manganese oxide nanostructures with controlled oxidation states and morphologies

Energy Technology Data Exchange (ETDEWEB)

Oba, Manabu; Oaki, Yuya; Imai, Hiroaki [Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522 (Japan)

2010-12-21

Manganese oxide nanostructures are synthesized by a route inspired by microbial mineralization in nature. The combination of organic molecules, which include antioxidizing and chelating agents, facilitates the parallel control of oxidation states and morphologies in an aqueous solution at room temperature. Divalent manganese hydroxide (Mn(OH){sub 2}) is selectively obtained as a stable dried powder by using a combination of ascorbic acid as an antioxidizing agent and other organic molecules with the ability to chelate to manganese ions. The topotactic oxidation of the resultant Mn(OH){sub 2} leads to the selective formation of trivalent manganese oxyhydroxide ({beta}-MnOOH) and trivalent/tetravalent sodium manganese oxide (birnessite, Na{sub 0.55}Mn{sub 2}O{sub 4}.1.5H{sub 2}O). For microbial mineralization in nature, similar synthetic routes via intermediates have been proposed in earlier works. Therefore, these synthetic routes, which include in the present study the parallel control over oxidation states and morphologies of manganese oxides, can be regarded as new biomimetic routes for synthesis of transition metal oxide nanostructures. As a potential application, it is demonstrated that the resultant {beta}-MnOOH nanostructures perform as a cathode material for lithium ion batteries. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

A Generalizable Top-Down Nanostructuring Method of Bulk Oxides: Sequential Oxygen-Nitrogen Exchange Reaction.

Science.gov (United States)

Lee, Lanlee; Kang, Byungwuk; Han, Suyoung; Kim, Hee-Eun; Lee, Moo Dong; Bang, Jin Ho

2018-05-27

A thermal reaction route that induces grain fracture instead of grain growth is devised and developed as a top-down approach to prepare nanostructured oxides from bulk solids. This novel synthesis approach, referred to as the sequential oxygen-nitrogen exchange (SONE) reaction, exploits the reversible anion exchange between oxygen and nitrogen in oxides that is driven by a simple two-step thermal treatment in ammonia and air. Internal stress developed by significant structural rearrangement via the formation of (oxy)nitride and the creation of oxygen vacancies and their subsequent combination into nanopores transforms bulk solid oxides into nanostructured oxides. The SONE reaction can be applicable to most transition metal oxides, and when utilized in a lithium-ion battery, the produced nanostructured materials are superior to their bulk counterparts and even comparable to those produced by conventional bottom-up approaches. Given its simplicity and scalability, this synthesis method could open a new avenue to the development of high-performance nanostructured electrode materials that can meet the industrial demand of cost-effectiveness for mass production. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Recent Advances in Metal Chalcogenides (MX; X = S, Se) Nanostructures for Electrochemical Supercapacitor Applications: A Brief Review

Science.gov (United States)

Theerthagiri, Jayaraman; Durai, Govindarajan; Rana, Abu ul Hassan Sarwar; Sangeetha, Kirubanandam; Kuppusami, Parasuraman; Kim, Hyun-Seok

2018-01-01

Supercapacitors (SCs) have received a great deal of attention and play an important role for future self-powered devices, mainly owing to their higher power density. Among all types of electrical energy storage devices, electrochemical supercapacitors are considered to be the most promising because of their superior performance characteristics, including short charging time, high power density, safety, easy fabrication procedures, and long operational life. An SC consists of two foremost components, namely electrode materials, and electrolyte. The selection of appropriate electrode materials with rational nanostructured designs has resulted in improved electrochemical properties for high performance and has reduced the cost of SCs. In this review, we mainly spotlight the non-metallic oxide, especially metal chalcogenides (MX; X = S, Se) based nanostructured electrode materials for electrochemical SCs. Different non-metallic oxide materials are highlighted in various categories, such as transition metal sulfides and selenides materials. Finally, the designing strategy and future improvements on metal chalcogenide materials for the application of electrochemical SCs are also discussed. PMID:29671823

Frontiers of 4d- and 5d-transition metal oxides

CERN Document Server

Cao, Gang

2013-01-01

This book is aimed at advanced undergraduates, graduate students and other researchers who possess an introductory background in materials physics and/or chemistry, and an interest in the physical and chemical properties of novel materials, especially transition metal oxides.New materials often exhibit novel phenomena of great fundamental and technological importance. Contributing authors review the structural, physical and chemical properties of notable 4d- and 5d-transition metal oxides discovered over the last 10 years. These materials exhibit extraordinary physical properties that differ s

Band gap tuning in transition metal oxides by site-specific substitution

Science.gov (United States)

Lee, Ho Nyung; Chisholm, Jr., Matthew F; Jellison, Jr., Gerald Earle; Singh, David J; Choi, Woo Seok

2013-12-24

A transition metal oxide insulator composition having a tuned band gap includes a transition metal oxide having a perovskite or a perovskite-like crystalline structure. The transition metal oxide includes at least one first element selected form the group of Bi, Ca, Ba, Sr, Li, Na, Mg, K, Pb, and Pr; and at least one second element selected from the group of Ti, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Hf, Ta, W, Re, Os, Ir, and Pt. At least one correlated insulator is integrated into the crystalline structure, including REMO.sub.3, wherein RE is at least one Rare Earth element, and wherein M is at least one element selected from the group of Co, V, Cr, Ni, Mn, and Fe. The composition is characterized by a band gap of less of 4.5 eV.

Structurally triggered metal-insulator transition in rare-earth nickelates.

Science.gov (United States)

Mercy, Alain; Bieder, Jordan; Íñiguez, Jorge; Ghosez, Philippe

2017-11-22

Rare-earth nickelates form an intriguing series of correlated perovskite oxides. Apart from LaNiO 3 , they exhibit on cooling a sharp metal-insulator electronic phase transition, a concurrent structural phase transition, and a magnetic phase transition toward an unusual antiferromagnetic spin order. Appealing for various applications, full exploitation of these compounds is still hampered by the lack of global understanding of the interplay between their electronic, structural, and magnetic properties. Here we show from first-principles calculations that the metal-insulator transition of nickelates arises from the softening of an oxygen-breathing distortion, structurally triggered by oxygen-octahedra rotation motions. The origin of such a rare triggered mechanism is traced back in their electronic and magnetic properties, providing a united picture. We further develop a Landau model accounting for the metal-insulator transition evolution in terms of the rare-earth cations and rationalizing how to tune this transition by acting on oxygen rotation motions.

Magnetic Ground State Properties of Transition Metals

DEFF Research Database (Denmark)

Andersen, O. K.; Madsen, J.; Poulsen, U. K.

1977-01-01

We review a simple one-electron theory of the magnetic and cohesive properties of ferro- and nearly ferromagnetic transition metals at 0 K. The theory is based on the density functional formalism, it makes use of the local spin density and atomic sphere approximations and it may, with further app...

High coercivity rare earth-transition metal magnets

International Nuclear Information System (INIS)

Croat, J.J.

1982-01-01

Ferromagnetic compositions having intrinsic magnetic coercivities at room temperature of at least 1,000 Oersteds are formed by the controlled quenching of molten rare earth-transition metal alloys. Hard magnets may be inexpensively formed from the lower atomic weight lanthanide elements and iron. The preferable compositions lie within: at least one of Fe, Ni, Co; 20 - 70 atomic percent: at least one of Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Y; 80 - 30 atomic percent. (author)

Formation of iron oxides from acid mine drainage and magnetic separation of the heavy metals adsorbed iron oxides

Energy Technology Data Exchange (ETDEWEB)

Kwon, Hee Won; Kim, Jeong Jin; Kim, Young Hun [Andong National University, Andong (Korea, Republic of); Ha, Dong Woo [Korea Electrotechnology Research Institute, Changwon (Korea, Republic of)

2016-03-15

There are a few thousand abandoned metal mines in South Korea. The abandoned mines cause several environmental problems including releasing acid mine drainage (AMD), which contain a very high acidity and heavy metal ions such as Fe, Cu, Cd, Pb, and As. Iron oxides can be formed from the AMD by increasing the solution pH and inducing precipitation. Current study focused on the formation of iron oxide in an AMD and used the oxide for adsorption of heavy metals. The heavy metal adsorbed iron oxide was separated with a superconducting magnet. The duration of iron oxide formation affected on the type of mineral and the degree of magnetization. The removal rate of heavy metal by the adsorption process with the formed iron oxide was highly dependent on the type of iron oxide and the solution pH. A high gradient magnetic separation (HGMS) system successfully separated the iron oxide and harmful heavy metals.

High coercivity rare earth-transition metal magnets

International Nuclear Information System (INIS)

Croat, J.J.

1982-01-01

Ferromagnetic compositions having intrinsic magnetic coercivities at room temperature of at least 1,000 Oersteds are formed by the controlled quenching of molten rare earth -transition metal alloys. Hard magnets may be inexpensively formed from the lower atomic weight lanthanide elements and iron. The preferable compositions lie within: at least one of Fe, Ni, Co (20 to 70 atomic percent); and at least one of Ce, Pr, Na, Sm, Eu, Tb, Dy, Ho, Er, Tm, Y (80 to 30 atomic percent). (author)

Structure and magnetism of transition-metal implanted dilute magnetic semiconductors

CERN Document Server

Pereira, Lino; Temst, K; Araújo, JP; Wahl, U

The discovery of a dilute magnetic semiconductor (DMS) in which ferromagnetism is carrier-mediated and persists above room temperature is a critical step towards the development of semiconductor-based spintronics. Among the many types of DMS materials which have been investigated, the current research interest can be narrowed down to two main classes of materials: (1) narrow-gap III-V semiconductors, mostly GaAs and InAs, doped with Mn; (2) wide-gap oxides and nitrides doped with 3d transition metals, mostly Mn- and Co-doped ZnO and Mn-doped GaN. With a number of interesting functionalities deriving from the carrier-mediated ferromagnetism and demonstrated in various proof-of-concept devices, Mn-doped GaAs has become, among DMS materials, one of the best candidates for technological application. However, despite major developments over the last 15 years, the maximum Curie temperature (185 K) remains well below room temperature. On the other hand, wide-gap DMS materials appear to exhibit ferromagnetic behavior...

Methods for synthesizing metal oxide nanowires

Science.gov (United States)

Sunkara, Mahendra Kumar; Kumar, Vivekanand; Kim, Jeong H.; Clark, Ezra Lee

2016-08-09

A method of synthesizing a metal oxide nanowire includes the steps of: combining an amount of a transition metal or a transition metal oxide with an amount of an alkali metal compound to produce a mixture; activating a plasma discharge reactor to create a plasma discharge; exposing the mixture to the plasma discharge for a first predetermined time period such that transition metal oxide nanowires are formed; contacting the transition metal oxide nanowires with an acid solution such that an alkali metal ion is exchanged for a hydrogen ion on each of the transition metal oxide nanowires; and exposing the transition metal oxide nanowires to the plasma discharge for a second predetermined time period to thermally anneal the transition metal oxide nanowires. Transition metal oxide nanowires produced using the synthesis methods described herein are also provided.

Inherent health and environmental risk assessment of nanostructured metal oxide production processes.

Science.gov (United States)

Torabifard, Mina; Arjmandi, Reza; Rashidi, Alimorad; Nouri, Jafar; Mohammadfam, Iraj

2018-01-10

The health and environmental effects of chemical processes can be assessed during the initial stage of their production. In this paper, the Chemical Screening Tool for Exposure and Environmental Release (ChemSTEER) software was used to compare the health and environmental risks of spray pyrolysis and wet chemical techniques for the fabrication of nanostructured metal oxide on a semi-industrial scale with a capacity of 300 kg/day in Iran. The pollution sources identified in each production process were pairwise compared in Expert Choice software using indicators including respiratory damage, skin damage, and environmental damages including air, water, and soil pollution. The synthesis of nanostructured zinc oxide using the wet chemical technique (with 0.523 wt%) leads to lower health and environmental risks compared to when spray pyrolysis is used (with 0.477 wt%). The health and environmental risk assessment of nanomaterial production processes can help select safer processes, modify the operation conditions, and select or modify raw materials that can help eliminate the risks.

Optical and electrical experiments at some transition-metal oxide foil-electrolyte interfaces

International Nuclear Information System (INIS)

Sari, S.O.; Ahlgren, W.L.

1977-01-01

Metal-oxide layers formed from transition-metal foils oxidized by heating in air have been examined for their photoelectrolytic response. The metals examined are Y, Ti, Zr, Hf, V, Nb, Ta, Mo, W, and Pt. Weak photoeffects are observed for oxide layers of all of these metals. Sizable light-dependent oxygen gas evolution rates are found in Ti and also in W oxides. The spectral dependence of the oxygen response in these compounds is investigated, and interpretation is given of these experiments

Synthesis engineering of iron oxide raspberry-shaped nanostructures.

Science.gov (United States)

Gerber, O; Pichon, B P; Ihiawakrim, D; Florea, I; Moldovan, S; Ersen, O; Begin, D; Grenèche, J-M; Lemonnier, S; Barraud, E; Begin-Colin, S

2017-01-07

Magnetic porous nanostructures consisting of oriented aggregates of iron oxide nanocrystals display very interesting properties such as a lower oxidation state of magnetite, and enhanced saturation magnetization in comparison with individual nanoparticles of similar sizes and porosity. However, the formation mechanism of these promising nanostructures is not well understood, which hampers the fine tuning of their magnetic properties, for instance by doping them with other elements. Therefore the formation mechanism of porous raspberry shaped nanostructures (RSNs) synthesized by a one-pot polyol solvothermal method has been investigated in detail from the early stages by using a wide panel of characterization techniques, and especially by performing original in situ HR-TEM studies in temperature. A time-resolved study showed the intermediate formation of an amorphous iron alkoxide phase with a plate-like lamellar structure (PLS). Then, the fine investigation of PLS transformation upon heating up to 500 °C confirmed that the synthesis of RSNs involves two iron precursors: the starting one (hydrated iron chlorides) and the in situ formed iron alkoxide precursor which decomposes with time and heating and contributes to the growth step of nanostructures. Such an understanding of the formation mechanism of RSNs is necessary to envision efficient and rational enhancement of their magnetic properties.

The 1s x-ray absorption pre-edge structures in transition metal oxides

NARCIS (Netherlands)

de Groot, Frank|info:eu-repo/dai/nl/08747610X; Vanko, Gyoergy; Glatzel, Pieter

2009-01-01

We develop a general procedure to analyse the pre-edges in 1s x-ray absorption near edge structure (XANES) of transition metal oxides and coordination complexes. Transition metal coordination complexes can be described from a local model with one metal ion. The 1s 3d quadrupole transitions are

CeO2/rGO/Pt sandwich nanostructure: rGO-enhanced electron transmission between metal oxide and metal nanoparticles for anodic methanol oxidation of direct methanol fuel cells.

Science.gov (United States)

Yu, Xue; Kuai, Long; Geng, Baoyou

2012-09-21

Pt-based nanocomposites have been of great research interest. In this paper, we design an efficient MO/rGO/Pt sandwich nanostructure as an anodic electrocatalyst for DMFCs with combination of the merits of rigid structure of metallic oxides (MOs) and excellent electronic conductivity of reduced oxidized graphene (rGO) as well as overcoming their shortcomings. In this case, the CeO(2)/rGO/Pt sandwich nanostructure is successfully fabricated through a facile hydrothermal approach in the presence of graphene oxide and CeO(2) nanoparticles. This structure has a unique building architecture where rGO wraps up the CeO(2) nanoparticles and Pt nanoparticles are homogeneously dispersed on the surface of rGO. This novel structure endows this material with great electrocatalytic performance in methanol oxidation: it reduces the overpotential of methanol oxidation significantly and its electrocatalytic activity and stability are much enhanced compared with Pt/rGO, CeO(2)/Pt and Pt/C catalysts. This work supplies a unique MO/rGO/Pt sandwich nanostructure as an efficient way to improve the electrocatalytic performance, which will surely shed some light on the exploration of some novel structures of electrocatalyst for DMFCs.

Volcano Relation for the Deacon Process over Transition-Metal Oxides

DEFF Research Database (Denmark)

Studt, Felix; Abild-Pedersen, Frank; Hansen, Heine Anton

2010-01-01

We establish an activity relation for the heterogeneous catalytic oxidation of HCI (the Deacon Process) over rutile transition-metal oxide catalysts by combining density functional theory calculations (DFT) with microkinetic modeling. Linear energy relations for the elementary reaction steps...

Hierarchical oxide-based composite nanostructures for energy, environmental, and sensing applications

Science.gov (United States)

Gao, Pu-Xian; Shimpi, Paresh; Cai, Wenjie; Gao, Haiyong; Jian, Dunliang; Wrobel, Gregory

2011-02-01

Self-assembled composite nanostructures integrate various basic nano-elements such as nanoparticles, nanofilms and nanowires toward realizing multifunctional characteristics, which promises an important route with potentially high reward for the fast evolving nanoscience and nanotechnology. A broad array of hierarchical metal oxide based nanostructures have been designed and fabricated in our research group, involving semiconductor metal oxides, ternary functional oxides such as perovskites and spinels and quaternary dielectric hydroxyl metal oxides with diverse applications in efficient energy harvesting/saving/utilization, environmental protection/control, chemical sensing and thus impacting major grand challenges in the area of materials and nanotechnology. Two of our latest research activities have been highlighted specifically in semiconductor oxide alloy nanowires and metal oxide/perovskite composite nanowires, which could impact the application sectors in ultraviolet/blue lighting, visible solar absorption, vehicle and industry emission control, chemical sensing and control for vehicle combustors and power plants.

The electronic structure and magnetic interactions in the mixed transition-metal oxide La(Co,Ni)O{sub 3} studied by X-ray absorption spectroscopies

Energy Technology Data Exchange (ETDEWEB)

Huang, Meng-Jie

2016-11-11

Transition-metal oxides have attracted a lot of attention because they exhibit a variety of intriguing physical properties. Among the transition-metal oxides, LaCoO{sub 3} is a very special compound which shows different spin states and spin-state transitions. Further, the physical properties can be controlled by changing temperature, replacement of rare-earth element, electron- or hole-doping, or by applying strain. The ground state of LaCoO{sub 3} is a non-magnetic insulator because the lowest energy configuration is t{sub 2g}{sup 6}e{sub g}{sup 0} (S = 0). However, the partial substitution of Co by Ni in La(Co,Ni)O{sub 3} (LCNO) will induce a ferromagnetic behavior. A number of models have been proposed for explaining the nature of the magnetic behavior in the past decades, but it is still a puzzle. In order to understand the origin of the ferromagnetism in La(Co,Ni)O{sub 3}, I have studied the electronic structure and magnetic interaction in this compound in a very direct way: by using X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) along with multiplet simulations. Samples were synthesized by the sol-gel method and structurally and magnetically characterized by XRD and SQUID. XAS clearly indicates a mixed-valence state for both Co and Ni, with both valences increasing monotonously with Ni content, x. While the gradual spin-state transition of Co{sup 3+} from low-spin (LS) to high-spin (HS) is preserved for low x it is suppressed in the high Ni-content samples. Regarding the spin configuration of Ni we find it stabilized in a ''mixed'' spin state, unlike the purely LS state of Ni in LaNiO{sub 3}. XMCD identifies the element-specific contributions to the magnetic moment and interactions. In particular, we find that it must be the coexistence of the HS state in both Co{sup 3+} and Ni{sup 3+} that induces t{sub 2g}-based ferromagnetic interaction via a ''double-exchange-like'' mechanism. Other species

Magnetic phase transition induced by electrostatic gating in two-dimensional square metal-organic frameworks

Science.gov (United States)

Wang, Yun-Peng; Li, Xiang-Guo; Liu, Shuang-Long; Fry, James N.; Cheng, Hai-Ping

2018-03-01

We investigate theoretically magnetism and magnetic phase transitions induced by electrostatic gating of two-dimensional square metal-organic framework compounds. We find that electrostatic gating can induce phase transitions between homogeneous ferromagnetic and various spin-textured antiferromagnetic states. Electronic structure and Wannier function analysis can reveal hybridizations between transition-metal d orbitals and conjugated π orbitals in the organic framework. Mn-containing compounds exhibit a strong d -π hybridization that leads to partially occupied spin-minority bands, in contrast to compounds containing transition-metal ions other than Mn, for which electronic structure around the Fermi energy is only slightly spin split due to weak d -π hybridization and the magnetic interaction is of the Ruderman-Kittel-Kasuya-Yosida type. We use a ferromagnetic Kondo lattice model to understand the phase transition in Mn-containing compounds in terms of carrier density and illuminate the complexity and the potential to control two-dimensional magnetization.

Transition radiation in metal-metal multilayer nanostructures as a medical source of hard x-ray radiation

International Nuclear Information System (INIS)

Pokrovsky, A. L.; Kaplan, A. E.; Shkolnikov, P. L.

2006-01-01

We show that a periodic metal-metal multilayer nanostructure can serve as an efficient source of hard x-ray transition radiation. Our research effort is aimed at developing an x-ray source for medical applications, which is based on using low-energy relativistic electrons. The approach toward choosing radiator-spacer couples for the generation of hard x-ray resonant transition radiation by few-MeV electrons traversing solid multilayer structures for the energies of interest to medicine (30-50 keV) changes dramatically compared with that for soft x-ray radiation. We show that one of the main factors in achieving the required resonant line is the absence of the contrast of the refractive indices between the spacer and the radiator at the far wings of the radiation line; for that purpose, the optimal spacer, as a rule, should have a higher atomic number than the radiator. Having experimental goals in mind, we have considered also the unwanted effects due to bremsstrahlung radiation, absorption and scattering of radiated photons, detector-related issues, and inhibited coherence of transition radiation due to random deviation of spacing between the layers. Choosing as a model example a Mo-Ag radiator-spacer pair of materials, we demonstrate that the x-ray transition radiation line can be well resolved with the use of spatial and frequency filtering

Magnetic properties of partially oxidized Fe films

Science.gov (United States)

Garcia, Miguel Angel; Lopez-Dominguez, Victor; Hernando, Antonio

Hybrid magnetic nanostructures exhibit appealing properties due to interface and proximity effects. A simple and interesting system of hybrid magnetic nanomaterials are partially oxidized ferromagnetic films. We have fabricated Fe films by thermal evaporation and performed a partial oxidation to magnetite (Fe3O4) by annealing in air at different times and temperatures. The magnetic properties of the films evolve from those of pure metallic iron to pure magnetite, showing intermediate states where the proximity effects control the magnetic behavior. At some stages, the magnetization curves obtained by SQUID and MOKE magnetometry exhibit important differences due to the dissimilar contribution of both phases to the magneto-optical response of the system This work has been supported by the Ministerio Español de Economia y Competitividad (MINECO) MAT2013-48009-C4-1. V.L.D and M.A.G. acknowledges financial support from BBVA foundation.

Micro- and Nanostructured Metal Oxide Chemical Sensors for Volatile Organic Compounds

Science.gov (United States)

Alim, M. A.; Penn, B. G.; Currie, J. R., Jr.; Batra, A. K.; Aggarwal, M. D.

2008-01-01

Aeronautic and space applications warrant the development of chemical sensors which operate in a variety of environments. This technical memorandum incorporates various kinds of chemical sensors and ways to improve their performance. The results of exploratory investigation of the binary composite polycrystalline thick-films such as SnO2-WO3, SnO2-In2O3, SnO2-ZnO for the detection of volatile organic compound (isopropanol) are reported. A short review of the present status of the new types of nanostructured sensors such as nanobelts, nanorods, nanotube, etc. based on metal oxides is presented.

High-resolution structural studies of ultra-thin magnetic, transition metal overlayers and two-dimensional transition metal oxides using synchrotron radiation

International Nuclear Information System (INIS)

Kellar, S.A.; Lawrence Berkeley National Lab., CA

1997-05-01

This thesis report the surface-structure determination of three, ultra-thin magnetic transition-metal films, Fe/Au(100), Mn/Ni(100), and Mn/Cu(100) using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) and photoelectron holography. These structural studies are the first to use non-s initial states in the ARPEFS procedure. This thesis also reports an ARPEFS surface-structure determination of a two-dimensional transition-metal oxide, [(1 x 1)O/W(110)] x 12. The authors have analyzed the ARPFES signal from the Au 4f 7/5 core level of the Au(1 ML)/Fe(15 ML)/Au(100) system. The analysis shows that the Fe grows layer by layer with one monolayer of gold, acting as a surfactant, remaining on top of the growing Fe layers. These surface gold atoms sit in the four-fold hollow site, 1.67 ± 0.02 A above the iron surface. The grown Fe layer is very much like the bulk, bcc iron, with an interlayer spacing of 1.43 ± 0.03 A. Analysis of the Mn 3p ARPEFS signals from c(2 x 2)Mn/Ni(100) and c(2 x 2)Mn/Cu(100) shows that the Mn forms highly corrugated surface alloys. The corrugation of the Mn/Ni(100) and Mn/Cu(100) systems are 0.24 ± 0.02 A and 0.30 ± 0.04 A respectively. In both cases the Mn is sticking above the plane of the surface substrate atoms. For the Mn/Ni(100) system the first layer Ni is contracted 4% from the bulk value. The Mn/Cu(100) system shows bulk spacing for the substrate Cu. Photoelectron holography shows that the Mn/Ni interface is very abrupt with very little Mn leaking into the second layer, while the Mn/Cu(100) case has a significant amount of Mn leaking into the second layer. A new, five-element electrostatic electron lens was developed for hemispherical electron-energy analyzers. This lens system can be operated at constant transverse or constants angular magnification, and has been optimized for use with the very small photon-spot sizes. Improvements to the hemispherical electron-energy analyzer are also discussed

High-resolution structural studies of ultra-thin magnetic, transition metal overlayers and two-dimensional transition metal oxides using synchrotron radiation

Energy Technology Data Exchange (ETDEWEB)

Kellar, S.A. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Advanced Light Source Div.

1997-05-01

This thesis report the surface-structure determination of three, ultra-thin magnetic transition-metal films, Fe/Au(100), Mn/Ni(100), and Mn/Cu(100) using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) and photoelectron holography. These structural studies are the first to use non-s initial states in the ARPEFS procedure. This thesis also reports an ARPEFS surface-structure determination of a two-dimensional transition-metal oxide, [(1 x 1)O/W(110)] x 12. The authors have analyzed the ARPFES signal from the Au 4f{sub 7/5} core level of the Au(1 ML)/Fe(15 ML)/Au(100) system. The analysis shows that the Fe grows layer by layer with one monolayer of gold, acting as a surfactant, remaining on top of the growing Fe layers. These surface gold atoms sit in the four-fold hollow site, 1.67 {+-} 0.02 A above the iron surface. The grown Fe layer is very much like the bulk, bcc iron, with an interlayer spacing of 1.43 {+-} 0.03 A. Analysis of the Mn 3p ARPEFS signals from c(2 x 2)Mn/Ni(100) and c(2 x 2)Mn/Cu(100) shows that the Mn forms highly corrugated surface alloys. The corrugation of the Mn/Ni(100) and Mn/Cu(100) systems are 0.24 {+-} 0.02 A and 0.30 {+-} 0.04 A respectively. In both cases the Mn is sticking above the plane of the surface substrate atoms. For the Mn/Ni(100) system the first layer Ni is contracted 4% from the bulk value. The Mn/Cu(100) system shows bulk spacing for the substrate Cu. Photoelectron holography shows that the Mn/Ni interface is very abrupt with very little Mn leaking into the second layer, while the Mn/Cu(100) case has a significant amount of Mn leaking into the second layer. A new, five-element electrostatic electron lens was developed for hemispherical electron-energy analyzers. This lens system can be operated at constant transverse or constants angular magnification, and has been optimized for use with the very small photon-spot sizes. Improvements to the hemispherical electron-energy analyzer are also discussed.

On the behavior of Bronsted-Evans-Polanyi Relations for Transition Metal Oxides

Energy Technology Data Exchange (ETDEWEB)

Vojvodic, Aleksandra

2011-08-22

Versatile Broensted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site and the dissociating molecule. The slope of the BEP relation is strongly coupled to the adsorbate geometry in the transition state. If it is final state-like the dissociative chemisorption energy can be considered as a descriptor for the dissociation. If it is initial state-like, on the other hand, the dissociative chemisorption energy is not suitable as descriptor for the dissociation. Dissociation of molecules with strong intramolecular bonds belong to the former and molecules with weak intramolecular bonds to the latter group. We show, for the prototype system La-perovskites, that there is a 'cyclic' behavior in the transition state characteristics upon change of the active transition metal of the oxide.

Fabrication of Fiber Bragg Grating Coating with TiO2 Nanostructured Metal Oxide for Refractive Index Sensor

Directory of Open Access Journals (Sweden)

Shaymaa Riyadh Tahhan

2017-01-01

Full Text Available To increase the sensitivity of biosensor a new approach using an optical fiber Bragg grating (FBG coated with a suitable nanostructured metal oxide (NMO is proposed which is costly effective compared to other biosensors. Bragg grating was written on a D-shaped optical fiber by phase mask method using a 248 nm KrF excimer laser for a 5 min exposure time producing a grating with a period of 528 nm. Titanium dioxide (TiO2 nanostructured metal oxide was coated over the fiber for the purpose of increasing its sensing area. The etched D-shaped FBG was then coated with 312 nm thick TiO2 nanostructured layer to ensure propagating the radiation modes within the core. The final structure was used to sense deionized water and saline. The etched D-shaped FBG original sensitivity before coating to air-deionized water and to air-saline was 0.314 nm/riu and 0.142 nm/riu, respectively. After coating the sensitivity became 1.257 nm/riu for air-deionized water and 0.857 nm/riu for air-saline.

Calculation of the magnetic anisotropy energy and finite-temperature magnetic properties of transition-metal films

International Nuclear Information System (INIS)

Garibay-Alonso, R; Villasenor-Gonzalez, P; Dorantes-Davila, J; Pastor, G M

2004-01-01

The magnetic anisotropy energy at the interface (IMAE) of Co films deposited on the Pd(111) surface are determined in the framework of a self-consistent, real-space tight-binding method at zero temperature. Significant spin moments are induced at the Pd atoms at the interface which have an important influence on the observed reorientation transitions as a function of Co film thickness. Film-substrate hybridizations are therefore crucial for the magneto-anisotropic behaviour of thin transition-metal films deposited on metallic non-magnetic substrates. Furthermore, using a real-space recursive expansion of the local Green function and within the virtual-crystal approximation we calculate the magnetization curves and the Curie temperature T C for free-standing Fe films

Transition metal ions mediated tyrosine based short peptide amphiphile nanostructures inhibit bacterial growth.

Science.gov (United States)

Joshi, Khashti Ballabh; Singh, Ramesh; Mishra, Narendra Kumar; Kumar, Vikas; Vinayak, Vandana

2018-05-17

We report the design and synthesis of biocompatible small peptide based molecule for the controlled and targeted delivery of the encapsulated bioactive metal ions via transforming their internal nanostructures. Tyrosine based short peptide amphiphile (sPA) was synthesized which self-assembled into β-sheet like secondary structures. The self assembly of the designed sPA was modulated by using different bioactive transition metal ions which is confirmed by spectroscopic and microscopic techniques. These bioactive metal ions conjugated sPA hybrid structures are further used to develop antibacterial materials. It is due to the excellent antibacterial activity of zinc ions that the growth of clinically relevant bacteria such as E. Coli was inhibited in the presence of zinc-sPA conjugate. The bacterial test demonstrated that owing to high biocompatibility with bacterial cell, the designed sPA worked as metal ions delivery agent and therefore it can show great potential in locally addressing bacterial infections. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Insertion compounds of transition-metal and uranium oxides

International Nuclear Information System (INIS)

Chippindale, A.M.; Dickens, P.G.; Powell, A.V.

1991-01-01

Several transition-metal and actinide oxides, in which the metal occurs in a high oxidation state, have open covalent structures and are capable of incorporating alkali and other electropositive metals under mild conditions to form insertion compounds A x MO n . These are solids which have several features in common: Over a range of compositions, A x MO n exists as one or more stable or metastable phases in which the structure of the parent oxide MO n is largely retained and the insertion element A is accommodated interstitially. Insertion is accompanied by a redox process A=A i . + e - M in which M is reduced and the electronic properties of the parent oxide change to those typical of a mixed-valence compound. The insertion process xA + MO n = A x MO n can be reversed, at least to some extent, by chemical or electrochemical reaction, with retention of structure (topotactic reaction). This review concentrates on methods of synthesis, characterisation, crystal structure and thermochemistry of these insertion compounds. It updates and extends previous work. (author)

Lanthanide Single-Molecule Magnets Framed by Alkali Metals & Magnetic and Spectroscopic Studies of 3d Transition Metal Complexes

DEFF Research Database (Denmark)

Konstantatos, Andreas

-molecule magnets (SMMs). Starting from the archetype SMM Mn12 we present the details of the mechanisms governing the relaxation of the magnetization of these systems. In Chapter 2 we present our work on the coordination chemistry of lanthanides with a new Schiff-base ligand, H3L [(E)-3-((2-hydroxyphenyl...... complexes of M3+ or M2+ metal ions (M: 3d transition metal) with the preference to either approximate octahedral or trigonal prismatic coordination geometry. A detailed magnetic characterization for most of the complexes is presented where a trinuclear Co2+ cluster stands out for its pronounced SMM...

Holey two-dimensional transition metal oxide nanosheets for efficient energy storage

Science.gov (United States)

Peng, Lele; Xiong, Pan; Ma, Lu; Yuan, Yifei; Zhu, Yue; Chen, Dahong; Luo, Xiangyi; Lu, Jun; Amine, Khalil; Yu, Guihua

2017-04-01

Transition metal oxide nanomaterials are promising electrodes for alkali-ion batteries owing to their distinct reaction mechanism, abundant active sites and shortened ion diffusion distance. However, detailed conversion reaction processes in terms of the oxidation state evolution and chemical/mechanical stability of the electrodes are still poorly understood. Herein we explore a general synthetic strategy for versatile synthesis of various holey transition metal oxide nanosheets with adjustable hole sizes that enable greatly enhanced alkali-ion storage properties. We employ in-situ transmission electron microscopy and operando X-ray absorption structures to study the mechanical properties, morphology evolution and oxidation state changes during electrochemical processes. We find that these holey oxide nanosheets exhibit strong mechanical stability inherited from graphene oxide, displaying minimal structural changes during lithiation/delithiation processes. These holey oxide nanosheets represent a promising material platform for in-situ probing the electrochemical processes, and could open up opportunities in many energy storage and conversion systems.

Transition metal oxide loaded MCM catalysts for photocatalytic ...

Indian Academy of Sciences (India)

Transition metal oxide (TiO2, Fe2O3, CoO) loaded MCM-41 and MCM-48 were synthesized by a two-step .... washed consecutively with water and ethanol, and cal- cined at 823 K for 5 .... conversion was observed in 1 h when the reaction was.

Sea-urchin-like iron oxide nanostructures for water treatment

Energy Technology Data Exchange (ETDEWEB)

Lee, Hyun Uk, E-mail: leeho@kbsi.re.kr [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of); Lee, Soon Chang [Department of Fine Chemical Engineering and Applied Chemistry, Chungnam National University, Daejeon 305-764 (Korea, Republic of); Lee, Young-Chul [Department of Biological Engineering, College of Engineering, Inha University, Incheon 402-751 (Korea, Republic of); Vrtnik, Stane; Kim, Changsoo; Lee, SangGap [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of); Lee, Young Boo; Nam, Bora [Jeonju Center, Korea Basic Science Institute, Jeonju 561-756 (Korea, Republic of); Lee, Jae Won [Department of Energy Engineering, Dankook University, Cheonan 330-714 (Korea, Republic of); Park, So Young; Lee, Sang Moon [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of); Lee, Jouhahn, E-mail: jouhahn@kbsi.re.kr [Division of Materials Science, Korea Basic Science Institute, Daejeon 305-333 (Korea, Republic of)

2013-11-15

Highlights: • The u-MFN were synthesized via a ultrasound irradiation and/or calcinations process. • The u-MFN exhibited excellent adsorption capacities. • The u-MFN also displayed excellent adsorption of organic polluent after recycling. • The u-MFN has the potential to be used as an efficient adsorbent material. -- Abstract: To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe{sub 2}O{sub 3}/Fe{sub 3}O{sub 4} phase) nanostructures (called u-MFN) with large surface areas (94.1 m{sup 2} g{sup −1}) and strong magnetic properties (57.9 emu g{sup −1}) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g{sup −1}) and Cr(VI) (35.0 mg g{sup −1}) and the organic pollutant Congo red (109.2 mg g{sup −1}). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions.

Sea-urchin-like iron oxide nanostructures for water treatment

International Nuclear Information System (INIS)

Lee, Hyun Uk; Lee, Soon Chang; Lee, Young-Chul; Vrtnik, Stane; Kim, Changsoo; Lee, SangGap; Lee, Young Boo; Nam, Bora; Lee, Jae Won; Park, So Young; Lee, Sang Moon; Lee, Jouhahn

2013-01-01

Highlights: • The u-MFN were synthesized via a ultrasound irradiation and/or calcinations process. • The u-MFN exhibited excellent adsorption capacities. • The u-MFN also displayed excellent adsorption of organic polluent after recycling. • The u-MFN has the potential to be used as an efficient adsorbent material. -- Abstract: To obtain adsorbents with high capacities for removing heavy metals and organic pollutants capable of quick magnetic separation, we fabricated unique sea-urchin-like magnetic iron oxide (mixed γ-Fe 2 O 3 /Fe 3 O 4 phase) nanostructures (called u-MFN) with large surface areas (94.1 m 2 g −1 ) and strong magnetic properties (57.9 emu g −1 ) using a simple growth process and investigated their potential applications in water treatment. The u-MFN had excellent removal capabilities for the heavy metals As(V) (39.6 mg g −1 ) and Cr(VI) (35.0 mg g −1 ) and the organic pollutant Congo red (109.2 mg g −1 ). The u-MFN also displays excellent adsorption of Congo red after recycling. Because of its high adsorption capacity, fast adsorption rate, and quick magnetic separation from treated water, the u-MFN developed in the present study is expected to be an efficient magnetic adsorbent for heavy metals and organic pollutants in aqueous solutions

Optical excitations of transition-metal oxides under the orbital multiplicity effects

International Nuclear Information System (INIS)

Lee, J S; Kim, M W; Noh, T W

2005-01-01

We investigated optical excitations of transition-metal (TM) oxides with metal oxygen octahedra taking account of the orbital multiplicity effects. We predicted excitation energies of intersite d-d transitions and p-d transitions of TM oxides. We compared the evaluated excitation energies with reported experimental data, and found that they are in good agreement with each other. Moreover, we could demonstrate possible answers for a few long-standing problems of the low-frequency spectral features in some early 3d TM oxides: (i) the broad and multi-peak structures of the d-d transitions (ii) the low values (around 2 eV) of the d-d transition energies for some t 2g 1 and t 2g 2 systems, and (iii) the lack of the d-d transition below 4.0 eV region for LaCrO 3 , one of the t 2g 3 systems. These indicate that our approach considering the orbital multiplicity effects could provide good explanations of intriguing features in the optical spectra of some early TM oxides. In addition, we showed that optical spectroscopy can be useful as a powerful tool to investigate spin and/or orbital correlations in the TM ions. Finally, we discussed the implications of the orbital multiplicity in the Zannen-Sawatzky-Allen scheme, which has been used successfully to classify correlated electron systems

Scalable high-affinity stabilization of magnetic iron oxide nanostructures by a biocompatible antifouling homopolymer

KAUST Repository

Luongo, Giovanni; Campagnolo, Paola; Perez, Jose E.; Kosel, Jü rgen; Georgiou, Theoni K.; Regoutz, Anna; Payne, David J; Stevens, Molly M.; Ryan, Mary P.; Porter, Alexandra E; Dunlop, Iain E

2017-01-01

Iron oxide nanostructures have been widely developed for biomedical applications, due to their magnetic properties and biocompatibility. In clinical application, the stabilization of these nanostructures against aggregation and non-specific interactions is typically achieved using weakly anchored polysaccharides, with better-defined and more strongly anchored synthetic polymers not commercially adopted due to complexity of synthesis and use. Here, we show for the first time stabilization and biocompatibilization of iron oxide nanoparticles by a synthetic homopolymer with strong surface anchoring and a history of clinical use in other applications, poly(2-methacryloyloxyethy phosphorylcholine) (poly(MPC)). For the commercially important case of spherical particles, binding of poly(MPC) to iron oxide surfaces and highly effective individualization of magnetite nanoparticles (20 nm) are demonstrated. Next-generation high-aspect ratio nanowires (both magnetite/maghemite and core-shell iron/iron oxide) are furthermore stabilized by poly(MPC)-coating, with nanowire cytotoxicity at large concentrations significantly reduced. The synthesis approach is exploited to incorporate functionality into the poly(MPC) chain is demonstrated by random copolymerization with an alkyne-containing monomer for click-chemistry. Taking these results together, poly(MPC) homopolymers and random copolymers offer a significant improvement over current iron oxide nanoformulations, combining straightforward synthesis, strong surface-anchoring and well-defined molecular weight.

Scalable high-affinity stabilization of magnetic iron oxide nanostructures by a biocompatible antifouling homopolymer

KAUST Repository

Luongo, Giovanni

2017-10-12

Iron oxide nanostructures have been widely developed for biomedical applications, due to their magnetic properties and biocompatibility. In clinical application, the stabilization of these nanostructures against aggregation and non-specific interactions is typically achieved using weakly anchored polysaccharides, with better-defined and more strongly anchored synthetic polymers not commercially adopted due to complexity of synthesis and use. Here, we show for the first time stabilization and biocompatibilization of iron oxide nanoparticles by a synthetic homopolymer with strong surface anchoring and a history of clinical use in other applications, poly(2-methacryloyloxyethy phosphorylcholine) (poly(MPC)). For the commercially important case of spherical particles, binding of poly(MPC) to iron oxide surfaces and highly effective individualization of magnetite nanoparticles (20 nm) are demonstrated. Next-generation high-aspect ratio nanowires (both magnetite/maghemite and core-shell iron/iron oxide) are furthermore stabilized by poly(MPC)-coating, with nanowire cytotoxicity at large concentrations significantly reduced. The synthesis approach is exploited to incorporate functionality into the poly(MPC) chain is demonstrated by random copolymerization with an alkyne-containing monomer for click-chemistry. Taking these results together, poly(MPC) homopolymers and random copolymers offer a significant improvement over current iron oxide nanoformulations, combining straightforward synthesis, strong surface-anchoring and well-defined molecular weight.

The electronic and optical properties of germanium tellurite glasses containing various transition metal oxides

International Nuclear Information System (INIS)

Khan, M.N.

1988-01-01

Various transition metal oxides, such as TiO 2 , V 2 O 5 , NiO, CuO, and ZnO are added to germanium-tellurite glass and measurements are reported of the electrical conductivity, density, optical absorption, infra-red absorption spectra, and electron spin resonance. It is found that the d.c. conductivity of glasses containing the same amount of V 2 O 5 is higher than that of germanium tellurite glasses containing a similar amount of other transition metal oxides, and is due to hopping between localized states. The optical absorption measurements show that the fundamental absorption edge is a function of glass composition and the optical absorption is due to forbidden indirect transitions. From the infra-red absorption spectra, it is found that the addition of transition metal oxides does not introduce any new absorption band in the infra-red spectrum of germanium tellurite glasses. A small shift of existing absorptions toward higher wave number is observed. The ESR measurements revealed that some transition metal ions are diamagnetic while others are paramagnetic in the glass network. (author)

Study of morphology effects on magnetic interactions and band gap variations for 3d late transition metal bi-doped ZnO nanostructures by hybrid DFT calculations

Energy Technology Data Exchange (ETDEWEB)

Datta, Soumendu, E-mail: soumendu@bose.res.in; Baral, Sayan; Mookerjee, Abhijit [Department of Condensed Matter Physics and Material Sciences, S.N. Bose National Centre for Basic Sciences, JD Block, Sector-III, Salt Lake City, Kolkata 700 098 (India); Kaphle, Gopi Chandra [Central Department of Physics, Tribhuvan University, Kathmandu (Nepal)

2015-08-28

Using density functional theory (DFT) based electronic structure calculations, the effects of morphology of semiconducting nanostructures on the magnetic interaction between two magnetic dopant atoms as well as a possibility of tuning band gaps have been studied in the case of the bi-doped (ZnO){sub 24} nanostructures with the impurity dopant atoms of the 3d late transition metals—Mn, Fe, Co, Ni, and Cu. To explore the morphology effect, three different structures of the host (ZnO){sub 24} nano-system, having different degrees of spatial confinement, have been considered: a two dimensional nanosheet, a one dimensional nanotube, and a finite cage-shaped nanocluster. The present study employs hybrid density functional theory to accurately describe the electronic structure of all the systems. It is shown here that the magnetic coupling between the two dopant atoms remains mostly anti-ferromagnetic in the course of changing the morphology from the sheet geometry to the cage-shaped geometry of the host systems, except for the case of energetically most stable bi-Mn doping, which shows a transition from ferromagnetic to anti-ferromagnetic coupling with decreasing aspect ratio of the host system. The effect of the shape change, however, has a significant effect on the overall band gap variations of both the pristine as well as all the bi-doped systems, irrespective of the nature of the dopant atoms and provides a means for easy tunability of their optoelectronic properties.

Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

KAUST Repository

Cheng, Yingchun; Zhang, Q. Y.; Schwingenschlö gl, Udo

2014-01-01

We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we

Rapid Mapping of Lithiation Dynamics in Transition Metal Oxide Particles with Operando X-ray Absorption Spectroscopy

Science.gov (United States)

Nowack, Lea; Grolimund, Daniel; Samson, Vallerie; Marone, Federica; Wood, Vanessa

2016-02-01

Since the commercialization of lithium ion batteries (LIBs), layered transition metal oxides (LiMO2, where M = Co, Mn, Ni, or mixtures thereof) have been materials of choice for LIB cathodes. During cycling, the transition metals change their oxidation states, an effect that can be tracked by detecting energy shifts in the X-ray absorption near edge structure (XANES) spectrum. X-ray absorption spectroscopy (XAS) can therefore be used to visualize and quantify lithiation kinetics in transition metal oxide cathodes; however, in-situ measurements are often constrained by temporal resolution and X-ray dose, necessitating compromises in the electrochemistry cycling conditions used or the materials examined. We report a combined approach to reduce measurement time and X-ray exposure for operando XAS studies of lithium ion batteries. A highly discretized energy resolution coupled with advanced post-processing enables rapid yet reliable identification of the oxidation state. A full-field microscopy setup provides sub-particle resolution over a large area of battery electrode, enabling the oxidation state within many transition metal oxide particles to be tracked simultaneously. Here, we apply this approach to gain insights into the lithiation kinetics of a commercial, mixed-metal oxide cathode material, nickel cobalt aluminium oxide (NCA), during (dis)charge and its degradation during overcharge.

Leading research on super metal. 3. Amorphous and nanostructured metallic materials; Super metal no sendo kenkyu. 3. Kogata buzai

Energy Technology Data Exchange (ETDEWEB)

NONE

1996-03-01

Very fine structure control technique for amorphous and nanostructured metallic materials was reviewed to exceed the marginal performance of small metallic member materials. In Japan, high strength alloys and anticorrosion alloys are currently developed as an amorphous structure control technique, and ultra fine powder production and nano-compaction molding are studied for nanostructured materials. Fabrication of amorphous alloy wire materials and metal glass in USA are also introduced. Fabrication of metallic nanocrystals deposited within gas phase in Germany are attracting attention. The strength and abrasion resistance are remarkably enhanced by making nanostructured crystals and dispersing them. It may be most suitable to utilize amorphous and nanostructured metallic materials for earth-friendly materials having anticorrosion, and catalyst and biomaterial affinities, and also for magnetic materials. It is important for controlling micro-structures to clarify the formation mechanism of structures. For their processing techniques, the diversity and possibility are suggested, as to the condensation and solidification of gaseous and liquid phase metals, the molding and processing of very fine solid phase alloys, and the manufacturing members by heat treatment. 324 refs., 109 figs., 21 tabs.

Laser-driven coating of vertically aligned carbon nanotubes with manganese oxide from metal organic precursors for energy storage

Science.gov (United States)

Pérez del Pino, A.; György, E.; Alshaikh, I.; Pantoja-Suárez, F.; Andújar, J. L.; Pascual, E.; Amade, R.; Bertran-Serra, E.

2017-09-01

Carbon nanotubes-transition metal oxide systems are intensively studied due to their excellent properties for electrochemical applications. In this work, an innovative procedure is developed for the synthesis of vertically aligned multi-walled carbon nanotubes (VACNTs) coated with transition metal oxide nanostructures. VACNTs are grown by plasma enhanced chemical vapor deposition and coated with a manganese-based metal organic precursor (MOP) film based on manganese acetate solution. Subsequent UV pulsed laser irradiation induces the effective heating-decomposition of the MOP leading to the crystallization of manganese oxide nanostructures on the VACNT surface. The study of the morphology, structure and composition of the synthesized materials shows the formation of randomly oriented MnO2 crystals, with few nanometers in size, and to their alignment in hundreds of nm long filament-like structures, parallel to the CNT’s long axis. Electrochemical measurements reveal a significant increase of the specific capacitance of the MnO2-VACNT system (100 F g-1) as compared to the initial VACNT one (21 F g-1).

Method for converting uranium oxides to uranium metal

International Nuclear Information System (INIS)

Duerksen, W.K.

1988-01-01

A method for converting uranium oxide to uranium metal is described comprising the steps of heating uranium oxide in the presence of a reducing agent to a temperature sufficient to reduce the uranium oxide to uranium metal and form a heterogeneous mixture of a uranium metal product and oxide by-products, heating the mixture in a hydrogen atmosphere at a temperature sufficient to convert uranium metal in the mixture to uranium hydride, cooling the resulting uranium hydride-containing mixture to a temperature sufficient to produce a ferromagnetic transition in the uranium hydride, magnetically separating the cooled uranium hydride from the mixture, and thereafter heating the separated uranium hydride in an inert atmosphere to a temperature sufficient to convert the uranium hydride to uranium metal

A solution phase fabrication of magnetic nanoparticles encapsulated in carbon

International Nuclear Information System (INIS)

Wei Xianwen; Zhu Guoxing; Xia Chuanjun; Ye Yin

2006-01-01

To avoid high energy consumption, intensive use of hardware and high cost in the manufacture of nanoparticles encapsulated in carbon, a simple, efficient and economical solution-phase method for the fabrication of FeNi at C nanostructures has been explored. The reaction to the magnetic metal at C structures here is conducted at a relatively low temperature (160 deg. C) and this strategy can be transferred to prepare other transition metal at C core-shell nanostructures. The saturation magnetization of metal in metal at C nanostructures is similar to those of the corresponding buck metals. Magnetic metal at C nanostructures with magnetic metal nanoparticles inside and a functionalized carbon surface outside may not only provide the opportunity to tailor the magnetic properties for magnetic storage devices and therapeutics but also make possible the loading of other functional molecules (e.g. enzymes, antigens) for clinic diagnostics, molecular biology, bioengineering, and catalysis

Plasmonic percolation: Plasmon-manifested dielectric-to-metal transition

KAUST Repository

Chen, Huanjun

2012-08-28

Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ∼70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles. © 2012 American Chemical Society.

Plasmonic percolation: Plasmon-manifested dielectric-to-metal transition

KAUST Repository

Chen, Huanjun; Wang, Feng; Li, Kun; Woo, Katchoi; Wang, Jianfang; Li, Quan; Sun, Ling Dong; Zhang, Xixiang; Lin, Haiqing; YAN, Chunhua

2012-01-01

Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ∼70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles. © 2012 American Chemical Society.

Metal oxide core shell nanostructures as building blocks for efficient light emission (SISGR)

Energy Technology Data Exchange (ETDEWEB)

Chang, Jane P [Univ. of California, Los Angeles, CA (United States); Dorman, James [Univ. of California, Los Angeles, CA (United States); Cheung, Cyrus [Univ. of California, Los Angeles, CA (United States)

2016-01-12

The objective of this research is to synthesize core-shell nano-structured metal oxide materials and investigate their structural, electronic and optical properties to understand the microscopic pathways governing the energy conversion process, thereby controlling and improving their efficiency. Specifically, the goal is to use a single metal oxide core-shell nanostructure and a single excitation source to generate photons with long emission lifetime over the entire visible spectrum and when controlled at the right ratio, generating white light. In order to achieve this goal, we need to control the energy transfer between light emitting elements, which dictates the control of their interatomic spacing and spatial distribution. We developed an economical wet chemical process to form the nanostructured core and to control the thickness and composition of the shell layers. With the help from using DOE funded synchrotron radiation facility, we delineated the growth mechanism of the nano-structured core and the shell layers, thereby enhancing our understanding of structure-property relation in these materials. Using the upconversion luminescence and the lifetime measurements as effective feedback to materials sysnthes is and integration, we demonstrated improved luminescence lifetimes of the core-shell nano-structures and quantified the optimal core-multi-shell structure with optimum shell thickness and composition. We developed a rare-earths co-doped LaPO₄ core-multishell structure in order to produce a single white light source. It was decided that the mutli-shell method would produce the largest increase in luminescence efficiency while limiting any energy transfer that may occur between the dopant ions. All samples resulted in emission spectra within the accepted range of white light generation based on the converted CIE color coordinates. The white light obtained varied between warm and cool white depending on the layering architecture, allowing for the

The Influence of Doping with Transition Metal Ions on the Structure and Magnetic Properties of Zinc Oxide Thin Films

Directory of Open Access Journals (Sweden)

Jenica Neamtu

2014-01-01

Full Text Available Zn1−xNixO (x=0.03÷0.10 and Zn1−xFexO (x=0.03÷0.15 thin films were synthesized by sol-gel method. The structure and the surface morphology of zinc oxide thin films doped with transition metal (TM ions have been investigated by X-ray diffraction (XRD and atomic force microscopy (AFM. The magnetic studies were done using vibrating sample magnetometer (VSM at room temperature. Experimental results revealed that the substitution of Ni ions in ZnO wurtzite lattice for the contents x=0.03÷0.10 (Ni2+ leads to weak ferromagnetism of thin films. For Zn1-xFexO with x=0.03÷0.05, the Fe3+ ions are magnetic coupling by superexchange interaction via oxygen ions in wurtzite structure. For x=0.10÷0.15 (Fe3+ one can observe the increasing of secondary phase of ZnFe2O4 spinel. The Zn0.9Fe0.1O film shows a superparamagnetic behavior due to small crystallite sizes and the net spin magnetic moments arisen from the interaction between the iron ions through an oxygen ion in the spinel structure.

Magnetic states, correlation effects and metal-insulator transition in FCC lattice

Science.gov (United States)

Timirgazin, M. A.; Igoshev, P. A.; Arzhnikov, A. K.; Irkhin, V. Yu

2016-12-01

The ground-state magnetic phase diagram (including collinear and spiral states) of the single-band Hubbard model for the face-centered cubic lattice and related metal-insulator transition (MIT) are investigated within the slave-boson approach by Kotliar and Ruckenstein. The correlation-induced electron spectrum narrowing and a comparison with a generalized Hartree-Fock approximation allow one to estimate the strength of correlation effects. This, as well as the MIT scenario, depends dramatically on the ratio of the next-nearest and nearest electron hopping integrals {{t}\\prime}/t . In contrast with metallic state, possessing substantial band narrowing, insulator one is only weakly correlated. The magnetic (Slater) scenario of MIT is found to be superior over the Mott one. Unlike simple and body-centered cubic lattices, MIT is the first order transition (discontinuous) for most {{t}\\prime}/t . The insulator state is type-II or type-III antiferromagnet, and the metallic state is spin-spiral, collinear antiferromagnet or paramagnet depending on {{t}\\prime}/t . The picture of magnetic ordering is compared with that in the standard localized-electron (Heisenberg) model.

CPA theory of the magnetization in rare earth transition metal alloys

International Nuclear Information System (INIS)

Szpunar, B.; Lindgaard, P.A.

1976-11-01

Calculations were made of the magnetic moment per atom of the transition metal and the rare earth metal in the intermetallic compounds, Gdsub(1-x)Nisub(x), Gdsub(1-x)Fesub(x), Gdsub(1-x)Cosub(x), and Ysub(1-x)Cosub(x). A simple model of the disordered alloy consisting of spins localized on the rare earth atoms and interacting with a narrow d-band is considered. The magnetic moment of the alloy at zero temperature is calculated within the molecular field and Hartree-Fock approximations. Disorder is treated in the coherent potential approximation. Results are in good agreement with the experimental data obtained for the crystalline and amorphous intermetallic compounds. It is shown that the temperature dependence of the magnetic moments and Curie and ferrimagnetic compensation temperatures can be accounted for by a simple model assuming a RKKY interaction between the rare-earth moments and the transition metal pseudo spin. The interaction is mediated by an effective alloy medium calculated using the CPA theory and elliptic densities of states. (Auth.)

Two-order parameters theory of the metal-insulator phase transition kinetics in the magnetic field

Science.gov (United States)

Dubovskii, L. B.

2018-05-01

The metal-insulator phase transition is considered within the framework of the Ginzburg-Landau approach for the phase transition described with two coupled order parameters. One of the order parameters is the mass density which variation is responsible for the origin of nonzero overlapping of the two different electron bands and the appearance of free electron carriers. This transition is assumed to be a first-order phase one. The free electron carriers are described with the vector-function representing the second-order parameter responsible for the continuous phase transition. This order parameter determines mostly the physical properties of the metal-insulator transition and leads to a singularity of the surface tension at the metal-insulator interface. The magnetic field is involved into the consideration of the system. The magnetic field leads to new singularities of the surface tension at the metal-insulator interface and results in a drastic variation of the phase transition kinetics. A strong singularity in the surface tension results from the Landau diamagnetism and determines anomalous features of the metal-insulator transition kinetics.

Nanostructures based on alumina hydroxides inhibit tumor growth

Science.gov (United States)

Fomenko, A. N.; Korovin, M. S.

2017-09-01

Nanoparticles and nanostructured materials are one of the most promising developments for cancer therapy. Gold nanoparticles, magnetic nanoparticles based on iron and its oxides and other metal oxides have been widely used in diagnosis and treatment of cancer. Much less research attention has been payed to nanoparticles and nanostructures based on aluminum oxides and hydroxides as materials for cancer diagnosis and treatment. However recent investigations have shown promising results regarding these objects. Here, we review the antitumor results obtained with AlOOH nanoparticles.

Electrical and Magnetic Properties of Binary Amorphous Transition Metal Alloys.

Science.gov (United States)

Liou, Sy-Hwang

The electrical, superconductive and magnetic properties of several binary transition metal amorphous and metastable crystalline alloys, Fe(,x)Ti(,100-x) (30 (LESSTHEQ) x (LESSTHEQ) 100), Fe(,x)Zr(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 93), Fe(,x)Hf(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 100), Fe(,x)Nb(,100 -x) (22 (LESSTHEQ) x (LESSTHEQ) 85), Ni(,x)Nb(,100-x) (20 (LESSTHEQ) x (LESSTHEQ) 80), Cu(,x)Nb(,100-x) (10 (LESSTHEQ) x (LESSTHEQ) 90) were studied over a wide composition range. Films were made using a magnetron sputtering system, and the structure of the films was investigated by energy dispersive x-ray diffraction. The composition region of each amorphous alloys system was determined and found in good agreement with a model proposed by Egami and Waseda. The magnetic properties and hyperfine interactions in the films were investigated using a conventional Mossbauer spectrometer and a ('57)Co in Rh matrix source. In all Fe-early transition metal binary alloys systems, Fe does not retain its moment in the low iron concentration region and the result is that the critical concentration for magnetic order (x(,c)) is much larger than anticipated from percolation considerations. A direct comparison between crystalline alloys and their amorphous counterparts of the same composition illustrate no clear correlation between crystalline and amorphous states. Pronounced discontinuities in the magnetic properties with variation in Fe content of all Fe-early transition metal alloys at phase boundaries separating amorphous and crystalline states have been observed. This is caused by the differences in the atomic arrangement and the electronic structure between crystalline and amorphous solids. The temperature dependence of resistivity, (rho)(T), of several binary amorphous alloys of Fe-TM (where TM = Ti, Zr, Hf, Nb etc.) has been studied from 2K to 300K. The Fe-poor (x x(,c)) samples have distinctive differences in (rho)(T) at low temperature (below 30K). All the magnetic samples

Synthesis and characterization of three-dimensional transition metal ions doped zinc oxide based dilute magnetic semiconductor thin films

Science.gov (United States)

Samanta, Kousik

Magnetic Polaron (BMP) model. The Resistivity of ZCO sample (˜ 103 O-cm) dropped by 5 orders of magnitude (0.02 O-cm) in Co, Al co-doped samples and the carrier concentrations increases 4 orders of magnitude (˜ 1019/cm3). The Cu2+ doped ZnO thin films showed the ferromagnetic property at 300K. The p-d orbital mixing of high spin Cu2+ (d9) state with the nearest neighbor oxygen p-orbital can explain the origin of RTFM in Zn 1-xCuxO thin films. The optical transmission spectroscopy and the photoluminescence spectroscopy analysis were used to understand the electronic band structure, near band edge (NBE) transition, and the excitonic behavior in ZnO and Zn1-xTMxO thin films. We have found the reduction of NBE transition at 300K due to the substitution of Co and Cu in ZnO host lattice. This narrowing of the optical band gap (NBE) is due to the sp-d exchange interaction between the d electrons of transition metal ions and the band electrons of ZnO; the strength of this interaction strongly depends on the number of d electrons. The s-d and p-d exchanges give rise to negative and positive corrections to the conduction and valance band edges respectively, leading to the NBE narrowing. We have observed the characteristic inter atomic d-d transitions in Co doped samples; thus confirming the substitution of Co2+ in the tetrahedral site in ZnO. The low temperature (77K) PL spectrum showed the basic excitonic characteristics of pure ZnO in Zn1-xTMxO thin films. The X-ray photoelectron spectroscopy (XPS) showed that the Co and Cu are normally in 2+ oxidation state, but in the case of higher Cu concentrations (>3%), the mixed state of Cu2+ and Cu1+ were detected.

Designing deoxidation inhibiting encapsulation of metal oxide nanostructures for fluidic and biological applications

Energy Technology Data Exchange (ETDEWEB)

Ghosh, Moumita, E-mail: ghoshiisc@gmail.com [Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012 (India); Centre for Nano Science and Engineering, Indian Institute of Science, Bangalore 560012 (India); IV. Institute of Physics, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); III. Institute of Physics – Biophysics and Complex Systems, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Ghosh, Siddharth [III. Institute of Physics – Biophysics and Complex Systems, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Seibt, Michael [IV. Institute of Physics, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Schaap, Iwan A.T. [III. Institute of Physics – Biophysics and Complex Systems, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Schmidt, Christoph F. [III. Institute of Physics – Biophysics and Complex Systems, Georg-August-Universität-Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Mohan Rao, G. [Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012 (India)

2016-12-30

Graphical abstract: To retain atomic structure and morphology of ZnO nanostructures (caused by deoxidation of ZnO) in water/bio-fluids, we propose and demonstrate a robust and inexpensive encapsulation technique using bio-compatible non-ionic surfactant. - Highlights: • Aqueous solutions of ZnO nanorods with and without surfactant are prepared. • With time ZnO nanorods show structural deterioration in different aqueous solutions. • Crystallinity of ZnO nanorods in absence of aqueous solution remain unaffected. • Encapsulation of bio-compatible surfactant in alchohol avoid ZnO deoxidation. • Crystallinity and structure of ZnO nanorods after encapsulation remain unaffected. - Abstract: Due to their photoluminescence, metal oxide nanostructures such as ZnO nanostructures are promising candidates in biomedical imaging, drug delivery and bio-sensing. To apply them as label for bio-imaging, it is important to study their structural stability in a bio-fluidic environment. We have explored the effect of water, the main constituent of biological solutions, on ZnO nanostructures with scanning electron microscopy (SEM) and photoluminescence (PL) studies which show ZnO nanorod degeneration in water. In addition, we propose and investigate a robust and inexpensive method to encapsulate these nanostructures (without structural degradation) using bio-compatible non-ionic surfactant in non-aqueous medium, which was not reported earlier. This new finding is an immediate interest to the broad audience of researchers working in biophysics, sensing and actuation, drug delivery, food and cosmetics technology, etc.

Analysis of magnetic correlations in layered or multiferroic transition element oxides using neutron diffraction

International Nuclear Information System (INIS)

Finger, Thomas

2013-01-01

Due to a great variety of physical phenomena the material class of transition metal oxides offers a large field of work for researchers, the more so as many underlying mechanisms are not understood yet. Of these materials a set of systems closely related to the manganates is investigated in this thesis via neutron scattering, emphasizing the analysis of magnetic correlations. It is shown, that for doping concentrations 0 ≤ x ≤ 0.5 the Co 2+ -ions in the layered cobaltates always exhibit a high-spin state with S = (3)/(2), whereas existing Co 3+ -ions adopt a low-spin state with S = 0 and stay non-magnetic. Furthermore, the magnetic correlations of three chiral multiferroics are investigated: Firstly, in MnWO 4 a memory effect is described; the crystal remembers its preceding chiral state even in the paramagnetic phase. In TbMnO 3 chiral fluctuations slightly above the multiferroic transition are investigated; it is possible to switch them by an applied external E-field. Finally, in DyMnO 3 the magnetic excitations are examined for the first time; they are comparable to those in TbMnO 3 .

Transition metal implanted ZnO. A correlation between structure and magnetism

Energy Technology Data Exchange (ETDEWEB)

Zhou, Shengqiang

2008-07-01

Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carriermediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases. (orig.)

Hybrid nanostructured materials with tunable magnetic characteristics

Energy Technology Data Exchange (ETDEWEB)

Torres-Martínez, Nubia E.; Garza-Navarro, M. A., E-mail: marco.garzanr@uanl.edu.mx; García-Gutiérrez, Domingo; González-González, Virgilio A.; Torres-Castro, Alejandro; Ortiz-Méndez, U. [Universidad Autónoma de Nuevo León, Facultad de Ingeniería Mecánica y Eléctrica (Mexico)

2014-12-15

We report on the development of hybrid nanostructured materials (HNM) based on spinel-metal-oxide nanoparticles (SMON) stabilized in carboxymethyl-cellulose (CMC)/cetyltrimethyl-ammonium-bromide (CTAB) templates, with tunable magnetic characteristics. These HNM were synthesized using a one-pot chemical approach to obtain CMC/CTAB templates with controllable size and morphology, where the SMON could be densely arranged. The synthesized HNM were characterized by transmission electron microscopy and its related techniques, such as bright field (BF) and Z-contrast (HAADF-STEM) imaging, and selected area electron diffraction, as well as static magnetic measuring. Experimental evidence suggests that the morphology and size of the CMC/CTAB templates are highly dependent on the weight ratio of CTAB:SMON, as well as the hydration days of the CMC that is used for the synthesis of the HNM. Controlling these parameters allows modifying the density of the SMON arrangement in the CMC/CTAB templates. Moreover, magnetic features such as remanence, coercivity, and blocking/de-blocking processes of the particles’ magnetic moments are highly dependent on the interactions among the SMON assembled in the templates. Hence, the magnetic characteristics of HNM can be modulated or tuned by controlling the manner the SMON are arranged within the CMC/CTAB templates.

Induced magnetism in transition metal intercalated graphitic systems

KAUST Repository

Kaloni, Thaneshwor P.; Schwingenschlö gl, Udo; Upadhyay Kahaly, M.

2011-01-01

We investigate the structure, chemical bonding, electronic properties, and magnetic behavior of a three-dimensional graphitic network in aba and aaa stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu). Using density functional theory, we find induced spin-polarization of the C atoms both when the graphene sheets are aba stacked (forming graphite) and aaa stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe, and Co turns out to vary from 1.38 μB to 4.10 μB, whereas intercalation of Ni and Cu does not lead to a magnetic state. The selective induction of spin-polarization can be utilized in spintronic and nanoelectronic applications.

Induced magnetism in transition metal intercalated graphitic systems

KAUST Repository

Kaloni, Thaneshwor P.

2011-10-26

We investigate the structure, chemical bonding, electronic properties, and magnetic behavior of a three-dimensional graphitic network in aba and aaa stacking with intercalated transition metal atoms (Mn, Fe, Co, Ni, and Cu). Using density functional theory, we find induced spin-polarization of the C atoms both when the graphene sheets are aba stacked (forming graphite) and aaa stacked (resembling bi-layer graphene). The magnetic moment induced by Mn, Fe, and Co turns out to vary from 1.38 μB to 4.10 μB, whereas intercalation of Ni and Cu does not lead to a magnetic state. The selective induction of spin-polarization can be utilized in spintronic and nanoelectronic applications.

The electronic structure and metal-insulator transitions in vanadium oxides

International Nuclear Information System (INIS)

Mossanek, Rodrigo Jose Ochekoski

2010-01-01

The electronic structure and metal-insulator transitions in vanadium oxides (SrVO_3, CaVO_3, LaVO_3 and YVO_3) are studied here. The purpose is to show a new interpretation to the spectra which is coherent with the changes across the metal-insulator transition. The main experimental techniques are the X-ray photoemission (PES) and X-ray absorption (XAS) spectroscopies. The spectra are interpreted with cluster model, band structure and atomic multiplet calculations. The presence of charge-transfer satellites in the core-level PES spectra showed that these vanadium oxides cannot be classified in the Mott-Hubbard regime. Further, the valence band and core-level spectra presented a similar behavior across the metal insulator transition. In fact, the structures in the spectra and their changes are determined by the different screening channels present in the metallic or insulating phases. The calculated spectral weight showed that the coherent fluctuations dominate the spectra at the Fermi level and give the metallic character to the SrVO_3 and CaVO_3 compounds. The vanishing of this charge fluctuation and the replacement by the Mott-Hubbard screening in the LaVO_3 and YVO_3 systems is ultimately responsible for the opening of a band gap and the insulating character. Further, the correlation effects are, indeed, important to the occupied electronic structure (coherent and incoherent peaks). On the other hand, the unoccupied electronic structure is dominated by exchange and crystal field effects (t2g and eg sub-bands of majority and minority spins). The optical conductivity spectrum was obtained by convoluting the removal and addition states. It showed that the oxygen states, as well as the crystal field and exchange effects are necessary to correctly compare and interpret the experimental results. Further, a correlation at the charge-transfer region of the core-level and valence band optical spectra was observed, which could be extended to other transition metal oxides

Synthesis, Characterization and Applications of One-Dimensional Metal Oxide Nanostructures

Science.gov (United States)

Santulli, Alexander

Nanomaterials have been of keen research interest, owing to their exciting and unique properties (e.g. optical, magnetic, electronic, and mechanical). These properties allow nanomaterials to have many applications in areas of medicine, alternative energy, catalysis, and information storage. In particular, one-dimensional (1D) nanomaterials are highly advantageous, owing to the inherent anisotropic nature, which allows for effective transport and study of properties on the nanoscale. More specifically, 1D metal oxide nanomaterials are of particular interest, owing to their high thermal and chemical stability, as well as their intriguing optical, electronic, and magnetic properties. Herein, we will investigate the synthesis and characterization of vanadium oxide, lithium niobate and chromium oxide. We will explore the methodologies utilized for the synthesis of these materials, as well as the overall properties of these unique nanomaterials. Furthermore, we will explore the application of titanium dioxide nanomaterials as the electron transport layer in dye sensitized solar cells (DSSCs), with an emphasis on the effect of the nanoscale morphology on the overall device efficiency.

Inverse spinel transition metal oxides for lithium-ion storage with different discharge/charge conversion mechanisms

International Nuclear Information System (INIS)

Wang, Jiawei; Ren, Yurong; Huang, Xiaobing; Ding, Jianning

2016-01-01

Highlights: • Inverse spinel structure relieves the irreversible phase transition of electrodes. • Anodes with the same structure show different discharge/charge conversion mechanisms. • High reversible capacity confirms the potential feasibility of composites. - Abstract: Inverse spinel transition metal oxides (Fe 3 O 4 , MnFe 2 O 4 , Fe 3 O 4 /reduced graphene oxide and MnFe 2 O 4 /reduced graphene oxide) are prepared by a facile ethylene-glycol-assisted hydrothermal method. The stability of inverse spinel structure and the high specific surface area of nanoscale provide transition metal oxides with high specific capacity. And the surface modification with reduced graphene oxide improves the poor conductivity of pristine transition metal oxides. Pristine Fe 3 O 4 and MnFe 2 O 4 deliver the high initial discharge capacity of 1137.1 and 1088.9 mAh g −1 , respectively. Fe 3 O 4 /reduced graphene oxide and MnFe 2 O 4 /reduced graphene oxide get the reversible capacity of 645.8 and 720 mAh g −1 , respectively, even after 55 cycles. The different discharge/charge conversion mechanisms make them different capacity stability. The great electrochemical performances of composites offer electrodes with suitable characteristics for high-performance energy storage application.

Transition-Metal-Controlled Inorganic Ligand-Supported Non-Precious Metal Catalysts for the Aerobic Oxidation of Amines to Imines.

Science.gov (United States)

Yu, Han; Zhai, Yongyan; Dai, Guoyong; Ru, Shi; Han, Sheng; Wei, Yongge

2017-10-09

Most state-of-art transition-metal catalysts usually require organic ligands, which are essential for controlling the reactivity and selectivity of reactions catalyzed by transition metals. However, organic ligands often suffer from severe problems including cost, toxicity, air/moisture sensitivity, and being commercially unavailable. Herein, we show a simple, mild, and efficient aerobic oxidation procedure of amines using inorganic ligand-supported non-precious metal catalysts 1, (NH 4 ) n [MMo 6 O 18 (OH) 6 ] (M=Cu 2+ ; Fe 3+ ; Co 3+ ; Ni 2+ ; Zn 2+ , n=3 or 4), synthesized by a simple one-step method in water at 100 °C, demonstrating that the catalytic activity and selectivity can be significantly improved by changing the central metal atom. In the presence of these catalysts, the catalytic oxidation of primary and secondary amines, as well as the coupling of alcohols and amines, can smoothly proceed to afford various imines with O 2 (1 atm) as the sole oxidant. In particular, the catalysts 1 have transition-metal ion core, and the planar arrangement of the six Mo VI centers at their highest oxidation states around the central heterometal can greatly enhance the Lewis acidity of catalytically active sites, and also enable the electrons in the center to delocalize onto the six edge-sharing MO 6 units, in the same way as ligands in traditional organometallic complexes. The versatility of this methodology maybe opens a path to catalytic oxidation through inorganic ligand-coordinated metal catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal Fluorides, Metal Chlorides and Halogenated Metal Oxides as Lewis Acidic Heterogeneous Catalysts. Providing Some Context for Nanostructured Metal Fluorides.

Science.gov (United States)

Lennon, David; Winfield, John M

2017-01-28

Aspects of the chemistry of selected metal fluorides, which are pertinent to their real or potential use as Lewis acidic, heterogeneous catalysts, are reviewed. Particular attention is paid to β-aluminum trifluoride, aluminum chlorofluoride and aluminas γ and η, whose surfaces become partially fluorinated or chlorinated, through pre-treatment with halogenating reagents or during a catalytic reaction. In these cases, direct comparisons with nanostructured metal fluorides are possible. In the second part of the review, attention is directed to iron(III) and copper(II) metal chlorides, whose Lewis acidity and potential redox function have had important catalytic implications in large-scale chlorohydrocarbons chemistry. Recent work, which highlights the complexity of reactions that can occur in the presence of supported copper(II) chloride as an oxychlorination catalyst, is featured. Although direct comparisons with nanostructured fluorides are not currently possible, the work could be relevant to possible future catalytic developments in nanostructured materials.

Application of nanodimensional particles and aluminum hydroxide nanostructures for cancer diagnosis and therapy

Science.gov (United States)

Korovin, M. S.; Fomenko, A. N.

2017-09-01

Nanoparticles and nanostructured materials are one of the most promising developments for cancer therapy. Gold nanoparticles, magnetic nanoparticles based on iron and its oxides and other metal oxides have been widely used in diagnosis and treatment of cancer. Much less researchers' attention has been paid to nanoparticles and nanostructures based on aluminum oxides and hydroxides as materials for cancer diagnosis and treatment. However, recent investigations have shown promising results regarding these objects. Here, we review the antitumor results obtained with different aluminum oxide/hydroxide nanoparticles and nanostructures.

Oxidation of Group 8 transition-Metal Hydrides and Ionic Hydrogenation of Ketones and Aldehydes

Energy Technology Data Exchange (ETDEWEB)

Smith, Kjell-Tore

1996-08-01

Transition-metal hydrides have received considerable attention during the last decades because of their unusual reactivity and their potential as homogeneous catalysts for hydrogenation and other reactions of organic substrates. An important class of catalytic processes where transition-metal hydrides are involved is the homogeneous hydrogenation of alkenes, alkynes, ketones, aldehydes, arenes and nitro compounds. This thesis studies the oxidation of Group 8 transition-metal hydrides and the ionic hydrogenation of ketones and aldehydes.

VUV photo-oxidation of gaseous benzene combined with ozone-assisted catalytic oxidation: Effect on transition metal catalyst

Science.gov (United States)

Huang, Haibao; Lu, Haoxian; Zhan, Yujie; Liu, Gaoyuan; Feng, Qiuyu; Huang, Huiling; Wu, Muyan; Ye, Xinguo

2017-01-01

Volatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O3, the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O3 catalytic decomposition and utilization. Benzene and O3 removal efficiency reached as high as 97% and 100% after 360 min, respectively. O3 was catalytically decomposed, generating highly reactive oxidants such as rad OH and rad O for benzene oxidation.

Optimization of film synthesized rare earth transition metal permanent magnet systems

International Nuclear Information System (INIS)

Cadieu, F.J.

1990-01-01

This report reviews work on the optimization of film synthesized rare earth transition metal permanent magnet systems. Topics include: high coercivity in Sm-Fe-Ti-V, Sm-Fe-V, and two element systems; ThMn 12 type pseudobinary SmFe 12 - X T X ; and sputter process control for the synthesis of precisely textured RE-TM magnetic films. (JL)

Electrodes synthesized from carbon nanostructures coated with a smooth and conformal metal adlayer

Science.gov (United States)

Adzic, Radoslav; Harris, Alexander

2014-04-15

High-surface-area carbon nanostructures coated with a smooth and conformal submonolayer-to-multilayer thin metal films and their method of manufacture are described. The preferred manufacturing process involves the initial oxidation of the carbon nanostructures followed by a surface preparation process involving immersion in a solution with the desired pH to create negative surface dipoles. The nanostructures are subsequently immersed in an alkaline solution containing a suitable quantity of non-noble metal ions which adsorb at surface reaction sites. The metal ions are then reduced via chemical or electrical means. The nanostructures are exposed to a solution containing a salt of one or more noble metals which replace adsorbed non-noble surface metal atoms by galvanic displacement. The process can be controlled and repeated to obtain a desired film coverage. The resulting coated nanostructures may be used, for example, as high-performance electrodes in supercapacitors, batteries, or other electric storage devices.

Sulfur-Hz(CHx)y(z = 0,1) functionalized metal oxide nanostructure decorated interfaces: Evidence of Lewis base and Brönsted acid sites – Influence on chemical sensing

International Nuclear Information System (INIS)

Laminack, William; Baker, Caitlin; Gole, James

2015-01-01

Nanostructure metal oxide decorated n-type extrinsic porous silicon (PS) semiconductor interfaces are modified through in-situ interaction with acidic ethane and butane thiols (EtSH, BuSH) and basic diethyl sulfide (Et 2 S). Highly sensitive conductometric sensor evaluations and X-ray Photoelectron Spectroscopy demonstrate the effect of sulfur group functionalization modifying the acidity of the metal oxides and their interaction with NH 3 . SEM micrographs demonstrate that the sulfur treated particles are less than 30 nm in size. EDAX studies confirm the chemical composition of the modified nanoparticles and suggest the surface interaction of the sulfides and thiols. The acidic thiols can form Brönsted acidic sites enhancing the acidity of the metal oxides, thus broadening the initial metal oxide acidity range. The sulfides interact to lower the Lewis acidity of nanostructured metal oxide sites. Conductometric response matrices with NH 3 at room temperature, corresponding to the thiol and sulfide treated nanostructures of the metal oxides TiO 2 , SnO x , Ni x O, Cu x O, and Au x O (x >> 1) are evaluated for a dominant electron transduction process forming the basis for reversible chemical sensing in the absence of chemical bond formation. Treatment with the acidic thiols enhances the metal center acidity. It is suggested that the thiols can interact to increase the Brönsted acidity of the doped metal oxide surface if they maintain SH bonds. This process may account for the shift in Lewis acidity as the Brönsted acid sites counter the decrease in Lewis acidity resulting from the interaction of S-(CH x ) y groups. In contrast, treatment with basic Et 2 S decreases the Lewis acidity of the metal oxide sites, enhancing the basicity of the decorated interface. XPS measurements indicate a change in binding energy (BE) of the metal and oxygen centers. The observed changes in conductometric response do not represent a simple increase in surface acidity or basicity but

Features of Magnetorefractive Effect in a [CoFe/Cu] n Multilayer Metallic Nanostructure

Science.gov (United States)

Yurasov, A. N.; Telegin, A. V.; Bannikova, N. S.; Milyaev, M. A.; Sukhorukov, Yu. P.

2018-02-01

The features of magnetorefractive effect (MRE) in metallic multilayer film Ni48Fe12Cr40(50 Å)/[Co90Fe10(14 Å)/Cu(22 Å)]8/Cr(20 Å) nanostructures, which exhibit giant magnetoresistance at room temperature, are investigated experimentally and theoretically. We show that the MRE in these structures reaches 1.5% in an applied magnetic field of 3.5 kOe, in a broad part of the IR region, and can change sign for both transmission and reflection of light. The refraction and extinction coefficients that are calculated for the nanostructures in an external magnetic field are in good agreement with our experimental data. The deduced formulas can be applied to estimating the MRE in multilayer metallic nanostructures.

Characterization of transition metal-containing oxide systems by Mössbauer Spectroscopy

Directory of Open Access Journals (Sweden)

Z. Homonnay

2004-12-01

Full Text Available High-temperature (high-Tc superconductors and colossal magnetoresistant (CMR materials belong to the most promising materials of the past 2-3 decades for technical applications. Most of them are oxides and the crucial element which determines their useful physical properties is often a transition metal (Cu, Co, Fe, Mn. 57Fe Mössbauer Spectroscopy can be used to characterize the electronic and structural properties of transition metal-containing oxides by providing information on the local electronic structure of the lattice site where the Mössbauer probe is accommodated. By reviewing several Mössbauer studies, it is demonstrated how the layered (2D electronic structure of high-Tc superconductors can be deduced from the analysis of the Mössbauer isomer shift and quadrupole splitting. We also show how the Mössbauer isomer shift indicates metallicity of the ferromagnetic phase in the CMR material LaxSr1-xCoO3.

Efficient photocarrier injection in a transition metal oxide heterostructure

CERN Document Server

Muraoka, Y; Ueda, Y; Hiroi, Z

2002-01-01

An efficient method for doping a transition metal oxide (TMO) with hole carriers is presented: photocarrier injection (PCI) in an oxide heterostructure. It is shown that an insulating vanadium dioxide (VO sub 2) film is rendered metallic under light irradiation by PCI from an n-type titanium dioxide (TiO sub 2) substrate doped with Nb. Consequently, a large photoconductivity, which is exceptional for TMOs, is found in the VO sub 2 /TiO sub 2 :Nb heterostructure. We propose an electronic band structure where photoinduced holes created in TiO sub 2 :Nb can be transferred into the filled V 3d band via the low-lying O 2p band of VO sub 2. (letter to the editor)

Electrical Switching in Thin Film Structures Based on Transition Metal Oxides

Directory of Open Access Journals (Sweden)

A. Pergament

2015-01-01

Full Text Available Electrical switching, manifesting itself in the nonlinear current-voltage characteristics with S- and N-type NDR (negative differential resistance, is inherent in a variety of materials, in particular, transition metal oxides. Although this phenomenon has been known for a long time, recent suggestions to use oxide-based switching elements as neuristor synapses and relaxation-oscillation circuit components have resumed the interest in this area. In the present review, we describe the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics.

Valley polarization in magnetically doped single-layer transition-metal dichalcogenides

KAUST Repository

Cheng, Yingchun

2014-04-28

We demonstrate that valley polarization can be induced and controlled in semiconducting single-layer transition-metal dichalcogenides by magnetic doping, which is important for spintronics, valleytronics, and photonics devices. As an example, we investigate Mn-doped MoS2 by first-principles calculations. We study how the valley polarization depends on the strength of the spin orbit coupling and the exchange interaction and discuss how it can be controlled by magnetic doping. Valley polarization by magnetic doping is also expected for other honeycomb materials with strong spin orbit coupling and the absence of inversion symmetry.

Magnetic properties of fcc Ni-based transition metal alloy

Czech Academy of Sciences Publication Activity Database

Kudrnovský, Josef; Drchal, Václav

2009-01-01

Roč. 100, č. 9 (2009), s. 1193-1196 ISSN 1862-5282 R&D Projects: GA MŠk OC 150; GA AV ČR IAA100100616 Institutional research plan: CEZ:AV0Z10100520 Keywords : transition metal alloys * Ni-based * pair exchange interactions * Curie temperatures * renormalized RPA Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.862, year: 2009

Chemical solution route to self-assembled epitaxial oxide nanostructures.

Science.gov (United States)

Obradors, X; Puig, T; Gibert, M; Queraltó, A; Zabaleta, J; Mestres, N

2014-04-07

Self-assembly of oxides as a bottom-up approach to functional nanostructures goes beyond the conventional nanostructure formation based on lithographic techniques. Particularly, chemical solution deposition (CSD) is an ex situ growth approach very promising for high throughput nanofabrication at low cost. Whereas strain engineering as a strategy to define nanostructures with tight control of size, shape and orientation has been widely used in metals and semiconductors, it has been rarely explored in the emergent field of functional complex oxides. Here we will show that thermodynamic modeling can be very useful to understand the principles controlling the growth of oxide nanostructures by CSD, and some attractive kinetic features will also be presented. The methodology of strain engineering is applied in a high degree of detail to form different sorts of nanostructures (nanodots, nanowires) of the oxide CeO2 with fluorite structure which then is used as a model system to identify the principles controlling self-assembly and self-organization in CSD grown oxides. We also present, more briefly, the application of these ideas to other oxides such as manganites or BaZrO3. We will show that the nucleation and growth steps are essentially understood and manipulated while the kinetic phenomena underlying the evolution of the self-organized networks are still less widely explored, even if very appealing effects have been already observed. Overall, our investigation based on a CSD approach has opened a new strategy towards a general use of self-assembly and self-organization which can now be widely spread to many functional oxide materials.

Nanostructural self-organization and dynamic adaptation of metal-polymer tribosystems

Science.gov (United States)

Mashkov, Yu. K.

2017-02-01

The results of investigating the effect of nanosize modifiers of a polymer matrix on the nanostructural self-organization of polymer composites and dynamic adaptation of metal-polymer tribosystems, which considerably affect the wear resistance of polymer composite materials, have been analyzed. It has been shown that the physicochemical nanostructural self-organization processes are developed in metal-polymer tribosystems with the formation of thermotropic liquid-crystal structures of the polymer matrix, followed by the transition of the system to the stationary state with a negative feedback that ensures dynamic adaptation of the tribosystem to given operating conditions.

Removal of Heavy Metals from Drinking Water by Magnetic Carbon Nanostructures Prepared from Biomass

Directory of Open Access Journals (Sweden)

Muhammad Muneeb Ur Rahman Khattak

2017-01-01

Full Text Available Heavy metals contamination of drinking water has significant adverse effects on human health due to their toxic nature. In this study a new adsorbent, magnetic graphitic nanostructures were prepared from watermelon waste. The adsorbent was characterized by different instrumental techniques (surface area analyzer, FTIR, XRD, EDX, SEM, and TG/DTA and was used for the removal of heavy metals (As, Cr, Cu, Pb, and Zn from water. The adsorption parameters were determined for heavy metals adsorption using Freundlich and Langmuir isotherms. The adsorption kinetics and effect of time, pH, and temperature on heavy metal ions were also determined. The best fits were obtained for Freundlich isotherm. The percent adsorption showed a decline at high pH. Best fit was obtained with second-order kinetics model for the kinetics experiments. The values of ΔH° and ΔG° were negative while that of ΔS° was positive. The prepared adsorbent has high adsorption capacities and can be efficiently used for the removal of heavy metals from water.

Increasing the solar cell power output by coating with transition metal-oxide nanorods

International Nuclear Information System (INIS)

Kuznetsov, I.A.; Greenfield, M.J.; Mehta, Y.U.; Merchan-Merchan, W.; Salkar, G.; Saveliev, A.V.

2011-01-01

Highlights: → Nanoparticles enhance solar cell efficiency. → Solar cell power increase by nanorod coating. → Metal-oxide nanorods are prepared in flames. → Molybdenum oxide nanorods effectively scatter light on solar cell surface. → Scattering efficiency depends on coating density. -- Abstract: Photovoltaic cells produce electric current through interactions among photons from an ambient light source and electrons in the semiconductor layer of the cell. However, much of the light incident on the panel is reflected or absorbed without inducing the photovoltaic effect. Transition metal-oxide nanoparticles, an inexpensive product of a process called flame synthesis, can cause scattering of light. Scattering can redirect photon flux, increasing the fraction of light absorbed in the thin active layer of silicon solar cells. This research aims to demonstrate that the application of transition metal-oxide nanorods to the surface of silicon solar panels can enhance the power output of the panels. Several solar panels were coated with a nanoparticle-methanol suspension, and the power outputs of the panels before and after the treatment were compared. The results demonstrate an increase in power output of up to 5% after the treatment. The presence of metal-oxide nanorods on the surface of the coated solar cells is confirmed by electron microscopy.

Magnetic properties of zigzag (0,9 GaAs nanotube doped with 3d transition metals

Directory of Open Access Journals (Sweden)

R Fathi

2016-06-01

Full Text Available of 3d transition metals (Sc, Ti, Cr, Mn , Fe, Co, Ni in both far and close situations were studied based on spin polarised density functional theory using the generalized gradient approximation (LDA with SIESTA code. The electronic structures show that zigzag (0,9 GaAs nanotubes are non-magnetic semiconductors with direct band gap. It was revealed that doping of 11.11 % Fe and Mn concentrations substituted in Ga sites in ferromagnetic phase in far situation and Cr sites in ferromagnetic phase in near situation introduces half metallic behavior with %100 spin polarization. The unique structure of spin polarised energy levels is primarily attributed to strong hybridization of 3d transition metal and its nearest-neighbor As-4p orbitals. The results of this study can be useful for empirical studies on diluted magnetic semiconductors (DMSs and systemic investigation in 3d transitional metals. We suggest that GaAs nanotubes doped by transition metals would have a potential application as a spin polarised electron source for spintronic devices in the future.

Hard X-ray photoemission spectroscopy of transition-metal oxide thin films and interfaces

International Nuclear Information System (INIS)

Wadati, H.; Fujimori, A.

2013-01-01

Highlights: •Photoemission spectroscopy is a powerful technique to study the electronic structures of transition-metal oxides. •Hard X-ray photoemission spectroscopy (HXPES) is a new type of photoemission spectroscopy which can probe bulk states. •HXPES is very suitable for studying oxide thin films such as the composition dependence and the film thickness dependence. -- Abstract: Photoemission spectroscopy is a powerful experimental technique to study the electronic structures of solids, especially of transition-metal oxides. Recently, hard X-ray photoemission spectroscopy (HXPES) has emerged as a more relevant experimental technique to obtain clear information about bulk states. Here, we describe how HXPES can be conveniently applied to study the interesting subjects on oxide thin films such as the composition dependence and the film thickness dependence of the electronic structures and the interfacial electronic structure of multilayers

Ethanol gas sensing performance of high-dimensional fuzz metal oxide nanostructure

Science.gov (United States)

Ibano, Kenzo; Kimura, Yoshihiro; Sugahara, Tohru; Lee, Heun Tae; Ueda, Yoshio

2018-04-01

Gas sensing ability of the He plasma induced fiber-like nanostructure, so-called fuzz structure, was firstly examined. A thin Mo layer deposited on a quartz surface was irradiated by He plasma to form the fuzz structure and oxidized by annealing in a quartz furnace. Electric conductivity of the fuzz Mo oxide layer was then measured through the Au electrodes deposited on the layer. Changes in electric conductivity by C2H5OH gas flow were examined as a function of temperature from 200 to 400 °C. Improved sensitivities were observed for the specimens after a fuzz nanostructure formation. However, the sensor developed in this study showed lower sensitivities than previously reported MoO3 nano-rod sensor, further optimization of oxidation is needed to improve the sensitivity.

Nanostructure-Directed Chemical Sensing: The IHSAB Principle and the Effect of Nitrogen and Sulfur Functionalization on Metal Oxide Decorated Interface Response

Directory of Open Access Journals (Sweden)

James L. Gole

2013-08-01

Full Text Available The response matrix, as metal oxide nanostructure decorated n-type semiconductor interfaces are modified in situ through direct amination and through treatment with organic sulfides and thiols, is demonstrated. Nanostructured TiO2, SnOx, NiO and CuxO (x = 1,2, in order of decreasing Lewis acidity, are deposited to a porous silicon interface to direct a dominant electron transduction process for reversible chemical sensing in the absence of significant chemical bond formation. The metal oxide sensing sites can be modified to decrease their Lewis acidity in a process appearing to substitute nitrogen or sulfur, providing a weak interaction to form the oxynitrides and oxysulfides. Treatment with triethylamine and diethyl sulfide decreases the Lewis acidity of the metal oxide sites. Treatment with acidic ethane thiol modifies the sensor response in an opposite sense, suggesting that there are thiol (SH groups present on the surface that provide a Brønsted acidity to the surface. The in situ modification of the metal oxides deposited to the interface changes the reversible interaction with the analytes, NH3 and NO. The observed change for either the more basic oxynitrides or oxysulfides or the apparent Brønsted acid sites produced from the interaction of the thiols do not represent a simple increase in surface basicity or acidity, but appear to involve a change in molecular electronic structure, which is well explained using the recently developed inverse hard and soft acids and bases (IHSAB model.

Metal Oxide Nanomaterial QNAR Models: Available Structural Descriptors and Understanding of Toxicity Mechanisms

Directory of Open Access Journals (Sweden)

Jiali Ying

2015-10-01

Full Text Available Metal oxide nanomaterials are widely used in various areas; however, the divergent published toxicology data makes it difficult to determine whether there is a risk associated with exposure to metal oxide nanomaterials. The application of quantitative structure activity relationship (QSAR modeling in metal oxide nanomaterials toxicity studies can reduce the need for time-consuming and resource-intensive nanotoxicity tests. The nanostructure and inorganic composition of metal oxide nanomaterials makes this approach different from classical QSAR study; this review lists and classifies some structural descriptors, such as size, cation charge, and band gap energy, in recent metal oxide nanomaterials quantitative nanostructure activity relationship (QNAR studies and discusses the mechanism of metal oxide nanomaterials toxicity based on these descriptors and traditional nanotoxicity tests.

Strongly Coupled Magnetic and Electronic Transitions in Multivalent Strontium Cobaltites.

Science.gov (United States)

Lee, J H; Choi, Woo Seok; Jeen, H; Lee, H-J; Seo, J H; Nam, J; Yeom, M S; Lee, H N

2017-11-22

The topotactic phase transition in SrCoO x (x = 2.5-3.0) makes it possible to reversibly transit between the two distinct phases, i.e. the brownmillerite SrCoO 2.5 that is a room-temperature antiferromagnetic insulator (AFM-I) and the perovskite SrCoO 3 that is a ferromagnetic metal (FM-M), owing to their multiple valence states. For the intermediate x values, the two distinct phases are expected to strongly compete with each other. With oxidation of SrCoO 2.5 , however, it has been conjectured that the magnetic transition is decoupled to the electronic phase transition, i.e., the AFM-to-FM transition occurs before the insulator-to-metal transition (IMT), which is still controversial. Here, we bridge the gap between the two-phase transitions by density-functional theory calculations combined with optical spectroscopy. We confirm that the IMT actually occurs concomitantly with the FM transition near the oxygen content x = 2.75. Strong charge-spin coupling drives the concurrent IMT and AFM-to-FM transition, which fosters the near room-T magnetic transition characteristic. Ultimately, our study demonstrates that SrCoO x is an intriguingly rare candidate for inducing coupled magnetic and electronic transition via fast and reversible redox reactions.

Optical response of nanostructured metal/dielectric composites and multilayers

Science.gov (United States)

Smith, Geoffrey B.; Maaroof, Abbas I.; Allan, Rodney S.; Schelm, Stefan; Anstis, Geoffrey R.; Cortie, Michael B.

2004-08-01

The homogeneous optical response in conducting nanostructured layers, and in insulating layers containing dense arrays of self assembled conducting nanoparticles separated by organic linkers, is examined experimentally through their effective complex indices (n*, k*). Classical effective medium models, modified to account for the 3-phase nanostructure, are shown to explain (n*, k*) in dense particulate systems but not inhomogeneous layers with macroscopic conductance for which a different approach to homogenisation is discussed. (n*, k*) data on thin granular metal films, thin mesoporous gold, and on thin metal layers containing ordered arrays of voids, is linked to properties of the surface plasmon states which span the nanostructured film. Coupling between evanescent waves at either surface counterbalanced by electron scattering losses must be considered. Virtual bound states for resonant photons result, with the associated transit delay leading to a large rise in n* in many nanostructures. Overcoating n-Ag with alumina is shown to alter (n*, k*) through its impact on the SP coupling. In contrast to classical optical homogenisation, effective indices depend on film thickness. Supporting high resolution SEM images are presented.

Using Dopants to Tune Oxygen Vacancy Formation in Transition Metal Oxide Resistive Memory.

Science.gov (United States)

Jiang, Hao; Stewart, Derek A

2017-05-17

Introducing dopants is an important way to tailor and improve electronic properties of transition metal oxides used as high-k dielectric thin films and resistance switching layers in leading memory technologies, such as dynamic and resistive random access memory (ReRAM). Ta 2 O 5 has recently received increasing interest because Ta 2 O 5 -based ReRAM demonstrates high switching speed, long endurance, and low operating voltage. However, advances in optimizing device characteristics with dopants have been hindered by limited and contradictory experiments in this field. We report on a systematic study on how various metal dopants affect oxygen vacancy formation in crystalline and amorphous Ta 2 O 5 from first principles. We find that isoelectronic dopants and weak n-type dopants have little impact on neutral vacancy formation energy and that p-type dopants can lower the formation energy significantly by introducing holes into the system. In contrast, n-type dopants have a deleterious effect and actually increase the formation energy for charged oxygen vacancies. Given the similar doping trend reported for other binary transition metal oxides, this doping trend should be universally valid for typical binary transition metal oxides. Based on this guideline, we propose that p-type dopants (Al, Hf, Zr, and Ti) can lower the forming/set voltage and improve retention properties of Ta 2 O 5 ReRAM.

Three-dimensional flowerlike iron oxide nanostructures: Morphology, composition and metal ion removal capability

Energy Technology Data Exchange (ETDEWEB)

Wang, Dan [School of Material Science and Engineering, University of Jinan, 250022 Jinan (China); Yang, Ping, E-mail: mse_yangp@ujn.edu.cn [School of Material Science and Engineering, University of Jinan, 250022 Jinan (China); Huang, Baibiao [State Key Laboratory of Crystal Materials, Shandong University, 250100 Jinan (China)

2016-01-15

Graphical abstract: The iron alkoxide precursors are calcined into α-Fe{sub 2}O{sub 3}, Fe{sub 3}O{sub 4} microstructures with different morphologies by changing calcination atmosphere, reaction time of precursors and calcination temperature simply. The Fe{sub 2}O{sub 3}/Ag hybrid composites prepared through aqueous synthesis and light irradiation. - Highlights: • α-Fe{sub 2}O{sub 3} and Fe{sub 3}O{sub 4} microstructures with different morphologies were created. • Solvents play an important role for the solvothermal treatment of precursors. • The α-Fe{sub 2}O{sub 3} microstructures show excellent adsorption properties. • Fe{sub 2}O{sub 3}/Ag hybrid composites were prepared to improve their properties. - Abstract: The flower-like precursors of Fe alkoxide constructed by the self-assembly of nanoflakes were prepared. Time-dependent experiments confirmed the formation mechanism of flower-like precursors. After calcination, α-Fe{sub 2}O{sub 3} and Fe{sub 3}O{sub 4} nanostructures with different morphologies were created. Fe{sub 3}O{sub 4} nanostructures containing blocks with a truncated octahedron structure were obtained under N{sub 2} protection. α-Fe{sub 2}O{sub 3} nanostructures were prepared in an air atmosphere. The values of maximum adsorption capacity of α-Fe{sub 2}O{sub 3} nanostructures for Cr{sup 6+} ions were much higher than that of commercial bulk α-Fe{sub 2}O{sub 3}. Ag NPs were deposited on α-Fe{sub 2}O{sub 3} nanostructures through an aqueous synthesis and light irradiation using L-cysteine as a linker. Such procedure is utilizable for the preparation of the composites of noble metals and magnetic materials.

Solid-state Water-mediated Transport Reduction of Nanostructured Iron Oxides

International Nuclear Information System (INIS)

Smirnov, Vladimir M.; Povarov, Vladimir G.; Voronkov, Gennadii P.; Semenov, Valentin G.; Murin, Igor' V.; Gittsovich, Viktor N.; Sinel'nikov, Boris M.

2001-01-01

The Fe 2+ /Fe 3+ ratio in two-dimensional iron oxide nanosructures (nanolayers with a thickness of 0.3-1.5 nm on silica surface) may be precisely controlled using the transport reduction (TR) technique. The species ≡-O-Fe(OH) 2 and (≡Si-O-) 2 -FeOH forming the surface monolayer are not reduced at 400-600 deg. C because of their covalent bonding to the silica surface, as demonstrated by Moessbauer spectroscopy. Iron oxide microparticles (microstructures) obtained by the impregnation technique, being chemically unbound to silica, are subjected to reduction at T ≥ 500 deg. C with formation of metallic iron in the form of α-Fe. Transport reduction of supported nanostructures (consisting of 1 or 4 monolayers) at T ≥ 600 deg. C produces bulk iron(II) silicate and metallic iron phases. The structural-chemical transformations occurring in transport reduction of supported iron oxide nanolayers are proved to be governed by specific phase processes in the nanostructures themselves

Studies of hyperfine magnetic fields in transition metals by radioactive ion implantation

International Nuclear Information System (INIS)

Kawase, Yoichi; Uehara, Shin-ichi; Nasu, Saburo; Ni Xinbo.

1994-01-01

In order to investigate hyperfine magnetic fields in transition metals by a time-differential perturbed angular correlation (TDPAC) technique, radioactive probes of 140 Cs obtained by KUR-ISOL have been implanted on transition metals of Fe, Ni and Co. Lamor precessions of 140 Ce used as a probe nucleus have been observed clearly and the hyperfine fields have been determined precisely corresponding to implanted sites in host metal. The irradiation effects caused by implantation have been examined by annealing the irradiated specimen at about 723 K. Some of the Lamor precessions have disappeared by the annealing. Discussions have been made on the occupied sites after implantation and the recovery process of induced damages by annealing. (author)

Metallic Nanostructures Based on DNA Nanoshapes

Directory of Open Access Journals (Sweden)

Boxuan Shen

2016-08-01

Full Text Available Metallic nanostructures have inspired extensive research over several decades, particularly within the field of nanoelectronics and increasingly in plasmonics. Due to the limitations of conventional lithography methods, the development of bottom-up fabricated metallic nanostructures has become more and more in demand. The remarkable development of DNA-based nanostructures has provided many successful methods and realizations for these needs, such as chemical DNA metallization via seeding or ionization, as well as DNA-guided lithography and casting of metallic nanoparticles by DNA molds. These methods offer high resolution, versatility and throughput and could enable the fabrication of arbitrarily-shaped structures with a 10-nm feature size, thus bringing novel applications into view. In this review, we cover the evolution of DNA-based metallic nanostructures, starting from the metallized double-stranded DNA for electronics and progress to sophisticated plasmonic structures based on DNA origami objects.

Structure-Reactivity Relationships in Multi-Component Transition Metal Oxide Catalysts FINAL Report

Energy Technology Data Exchange (ETDEWEB)

Altman, Eric I. [Yale Univ., New Haven, CT (United States)

2015-10-06

The focus of the project was on developing an atomic-level understanding of how transition metal oxide catalysts function. Over the course of several renewals the specific emphases shifted from understanding how local structure and oxidation state affect how molecules adsorb and react on the surfaces of binary oxide crystals to more complex systems where interactions between different transition metal oxide cations in an oxide catalyst can affect reactivity, and finally to the impact of cluster size on oxide stability and reactivity. Hallmarks of the work were the use of epitaxial growth methods to create surfaces relevant to catalysis yet tractable for fundamental surface science approaches, and the use of scanning tunneling microscopy to follow structural changes induced by reactions and to pinpoint adsorption sites. Key early findings included the identification of oxidation and reduction mechanisms on a tungsten oxide catalyst surface that determine the sites available for reaction, identification of C-O bond cleavage as the rate limiting step in alcohol dehydration reactions on the tungsten oxide surface, and demonstration that reduction does not change the favored reaction pathway but rather eases C-O bond cleavage and thus reduces the reaction barrier. Subsequently, a new reconstruction on the anatase phase of TiO₂ relevant to catalysis was discovered and shown to create sites with distinct reactivity compared to other TiO₂ surfaces. Building on this work on anatase, the mechanism by which TiO₂ enhances the reactivity of vanadium oxide layers was characterized and it was found that the TiO₂ substrate can force thin vanadia layers to adopt structures they would not ordinarily form in the bulk which in turn creates differences in reactivity between supported layers and bulk samples. From there, the work progressed to studying well-defined ternary oxides where synergistic effects between the two cations can induce

On the behavior of Brønsted-Evans-Polanyi relations for transition metal oxides

DEFF Research Database (Denmark)

Vojvodic, Aleksandra; Vallejo, Federico Calle; Guo, Wei

2011-01-01

Versatile Brønsted-Evans-Polanyi (BEP) relations are found from density functional theory for a wide range of transition metal oxides including rutiles and perovskites. For oxides, the relation depends on the type of oxide, the active site, and the dissociating molecule. The slope of the BEP...

Magnetic properties of nickel nanostructures grown in AAO membrane

International Nuclear Information System (INIS)

Oh, S.-L.; Kim, Y.-R.; Malkinski, L.; Vovk, A.; Whittenburg, S.L.; Kim, E.-M.; Jung, J.-S.

2007-01-01

One-dimensional nanostructures can be built by performing chemical or electrochemical reactions in the pores of a suitable host or matrix material. We have developed a method of electrodeposition of nickel nanostructures inside cylindrical pores of the anodic aluminum oxide (AAO) membranes, which provides precise control of the nanostructure height. We were able to fabricate hexagonal arrays of particles in the form of spheres, rods and long wires. Magnetization measurements of these nanostructures as function of field and temperature were carried out using a superconducting quantum-interference device magnetometer. The shape of nickel nanostructures has been investigated by field emission scanning electron microscope. The coercivity of the nickel nanostructures measured with the field perpendicular to the membrane was increasing with increasing aspect ratio of the nanostructures. These experimental values of the coercivity, varying from 200 Oe for the spherical nanodots to 730 Oe for the nanowires, are in a fair agreement with our micromagnetic modeling calculations

Magnetic properties of nickel nanostructures grown in AAO membrane

Energy Technology Data Exchange (ETDEWEB)

Oh, S -L [Department of Chemistry, Yonsei University, Seoul (Korea, Republic of); Kim, Y -R [Department of Chemistry, Yonsei University, Seoul (Korea, Republic of); Malkinski, L [Advanced Material Research Institute, University of New Orleans, New Orleans, LA 70148 (United States); Vovk, A [Advanced Material Research Institute, University of New Orleans, New Orleans, LA 70148 (United States); Whittenburg, S L [Advanced Material Research Institute, University of New Orleans, New Orleans, LA 70148 (United States); Kim, E -M [Korea Basic Science Institute, Kangnung 210-702 (Korea, Republic of); Jung, J -S [Department of Chemistry, Kangnung National University, Kangnung 210-702 (Korea, Republic of)

2007-03-15

One-dimensional nanostructures can be built by performing chemical or electrochemical reactions in the pores of a suitable host or matrix material. We have developed a method of electrodeposition of nickel nanostructures inside cylindrical pores of the anodic aluminum oxide (AAO) membranes, which provides precise control of the nanostructure height. We were able to fabricate hexagonal arrays of particles in the form of spheres, rods and long wires. Magnetization measurements of these nanostructures as function of field and temperature were carried out using a superconducting quantum-interference device magnetometer. The shape of nickel nanostructures has been investigated by field emission scanning electron microscope. The coercivity of the nickel nanostructures measured with the field perpendicular to the membrane was increasing with increasing aspect ratio of the nanostructures. These experimental values of the coercivity, varying from 200 Oe for the spherical nanodots to 730 Oe for the nanowires, are in a fair agreement with our micromagnetic modeling calculations.

La interstitial defect-induced insulator-metal transition in the oxide heterostructures LaAl O3 /SrTi O3

Science.gov (United States)

Zhou, Jun; Yang, Ming; Feng, Yuan Ping; Rusydi, Andrivo

2017-11-01

Perovskite oxide interfaces have attracted tremendous research interest for their fundamental physics and promising all-oxide electronic applications. Here, based on first-principles calculations, we propose a surface La interstitial promoted interface insulator-metal transition in LaAl O3 /SrTi O3 (110). Compared with surface oxygen vacancies, which play a determining role on the insulator-metal transition of LaAl O3 /SrTi O3 (001) interfaces, we find that surface La interstitials can be more experimentally realistic and accessible for manipulation and more stable in an ambient atmospheric environment. Interestingly, these surface La interstitials also induce significant spin-splitting states with a Ti dy z/dx z character at a conducting LaAl O3 /SrTi O3 (110) interface. On the other hand, for insulating LaAl O3 /SrTi O3 (110) (<4 unit cells LaAl O3 thickness), a distortion between La (Al) and O atoms is found at the LaAl O3 side, partially compensating the polarization divergence. Our results reveal the origin of the metal-insulator transition in LaAl O3 /SrTi O3 (110) heterostructures, and also shed light on the manipulation of the superior properties of LaAl O3 /SrTi O3 (110) for different possibilities in electronic and magnetic applications.

Hierarchical Assembly of Multifunctional Oxide-based Composite Nanostructures for Energy and Environmental Applications

Directory of Open Access Journals (Sweden)

Hui-Jan Lin

2012-06-01

Full Text Available Composite nanoarchitectures represent a class of nanostructured entities that integrates various dissimilar nanoscale building blocks including nanoparticles, nanowires, and nanofilms toward realizing multifunctional characteristics. A broad array of composite nanoarchitectures can be designed and fabricated, involving generic materials such as metal, ceramics, and polymers in nanoscale form. In this review, we will highlight the latest progress on composite nanostructures in our research group, particularly on various metal oxides including binary semiconductors, ABO₃-type perovskites, A₂BO₄ spinels and quaternary dielectric hydroxyl metal oxides (AB(OH₆ with diverse application potential. Through a generic template strategy in conjunction with various synthetic approaches—such as hydrothermal decomposition, colloidal deposition, physical sputtering, thermal decomposition and thermal oxidation, semiconductor oxide alloy nanowires, metal oxide/perovskite (spinel composite nanowires, stannate based nanocompostes, as well as semiconductor heterojunction—arrays and networks have been self-assembled in large scale and are being developed as promising classes of composite nanoarchitectures, which may open a new array of advanced nanotechnologies in solid state lighting, solar absorption, photocatalysis and battery, auto-emission control, and chemical sensing.

Open volume defects and magnetic phase transition in Fe{sub 60}Al{sub 40} transition metal aluminide

Energy Technology Data Exchange (ETDEWEB)

Liedke, M. O., E-mail: m.liedke@hzdr.de; Anwand, W.; Butterling, M.; Wagner, A. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Bali, R.; Cornelius, S.; Potzger, K. [Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Trinh, T. T. [Institute of Radiation Physics, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden (Germany); Technical University Dresden, Helmholtzstr. 10, 01609 Dresden (Germany); Salamon, S.; Walecki, D.; Smekhova, A.; Wende, H. [Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Lotharstraße 1, 47048 Duisburg (Germany)

2015-04-28

Magnetic phase transition in the Fe{sub 60}Al{sub 40} transition metal aluminide from the ferromagnetic disordered A2-phase to the paramagnetic ordered B2-phase as a function of annealing up to 1000 °C has been investigated by means of magneto-optical and spectroscopy techniques, i.e., Kerr effect, positron annihilation, and Mössbauer spectroscopy. The positron annihilation spectroscopy has been performed in-situ sequentially after each annealing step at the Apparatus for In-situ Defect Analysis that is a unique tool combining positron annihilation spectroscopy with temperature treatment, material evaporation, ion irradiation, and sheet resistance measurement techniques. The overall goal was to investigate the importance of the open volume defects onto the magnetic phase transition. No evidence of variation in the vacancy concentration in matching the magnetic phase transition temperature range (400–600 °C) has been found, whereas higher temperatures showed an increase in the vacancy concentration.

Chemically synthesized metal-oxide-metal segmented nanowires with high ferroelectric response

International Nuclear Information System (INIS)

Herderick, Edward D; Padture, Nitin P; Polomoff, Nicholas A; Huey, Bryan D

2010-01-01

A chemical synthesis method is presented for the fabrication of high-definition segmented metal-oxide-metal (MOM) nanowires in two different ferroelectric oxide systems: Au-BaTiO 3 -Au and Au-PbTiO 3 -Au. This method entails electrodeposition of segmented nanowires of Au-TiO 2 -Au inside anodic aluminum oxide (AAO) templates, followed by topotactic hydrothermal conversion of the TiO 2 segments into BaTiO 3 or PbTiO 3 segments. Two-terminal devices from individual MOM nanowires are fabricated, and their ferroelectric properties are measured directly, without the aid of scanning probe microscopy (SPM) methods. The MOM nanowire architecture provides high-quality end-on electrical contacts to the oxide segments, and allows direct measurement of properties of nanoscale volume, strain-free oxide segments. Unusually high ferroelectric responses, for chemically synthesized oxides, in these MOM nanowires are reported, and are attributed to the lack of residual strain in the oxides. The ability to measure directly the active properties of nanoscale volume, strain-free oxides afforded by the MOM nanowire architecture has important implications for fundamental studies of not only ferroelectric nanostructures but also nanostructures in the emerging field of multiferroics.

Strongly correlated electron systems and neutron scattering. Magnetism, superconductivity, structural phase transition

Energy Technology Data Exchange (ETDEWEB)

Katano, Susumu [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

1998-03-01

Neutron scattering experiments in our group on strongly correlated electron systems are reviewed Metal-insulator transitions caused by structural phase transitions in (La{sub 1-x}Sr{sub x}) MnO{sub 3}, a novel magnetic transition in the CeP compound, correlations between antiferromagnetism and superconductivity in UPd{sub 2}Al{sub 3} and so forth are discussed. Here, in this note, the phase transition of Mn-oxides was mainly described. (author)

Characterization of the porous anodic alumina nanostructures with a metal interlayer on Si substrates

Energy Technology Data Exchange (ETDEWEB)

Fang, Chia-Hui; Chen, Hung-Ing; Hsiao, Jui-Ju; Wang, Jen-Cheng; Nee, Tzer-En, E-mail: neete@mail.cgu.edu.tw

2014-04-15

Porous anodic alumina (PAA) films produced by the anodization technique have made possible the mass production of porous nano-scale structures where the pore height and diameter are controllable. A metal interlayer is observed to have a significant influence on the characteristics of these PAA nanostructures. In this study, we investigate in-depth the effect of the current density on the properties of porous anodic alumina nanostructures with a metal interlayer. A thin film layer of tungsten (W) and titanium (Ti) was sandwiched between a porous anodic alumina film and a silicon (Si) substrate to form PAA/W/Si and PAA/Ti/Si structures. The material and optical characteristics of the porous anodic alumina nanostructures, with and without a metal interlayer, on silicon substrates were studied using the scanning electron microscopy, X-ray diffraction (XRD), and temperature-dependent photoluminescence (PL) measurements. The current densities of the porous anodic alumina nanostructures with the metal interlayer are higher than for the PAA/Si, resulting in an increase of the growth rate of the oxide layer. It can be observed from the X-ray diffraction curves that there is more aluminum oxide inside the structure with the metal interlayer. Furthermore, it has been found that there is a reduction in the photoluminescence intensity of the oxygen vacancy with only one electron due to the formation of oxygen vacancies inside the aluminum oxide during the re-crystallization process. This leads to competition between the two kinds of different oxygen-deficient defect centers (F+ and F centers) in the carrier recombination mechanism from the PL spectra of the porous anodic alumina nanostructures, with and without a metal interlayer, on silicon substrates. -- Highlights: • Study of porous anodic alumina (PAA) films with metal interlayers on silicon. • The highly ordered PAA film with a fairly regular nano-porous structure. • The luminescence properties of PAA films were

Converged G W quasiparticle energies for transition metal oxide perovskites

Science.gov (United States)

Ergönenc, Zeynep; Kim, Bongjae; Liu, Peitao; Kresse, Georg; Franchini, Cesare

2018-02-01

The ab initio calculation of quasiparticle (QP) energies is a technically and computationally challenging problem. In condensed matter physics, the most widely used approach to determine QP energies is the G W approximation. Although the G W method has been widely applied to many typical semiconductors and insulators, its application to more complex compounds such as transition metal oxide perovskites has been comparatively rare, and its proper use is not well established from a technical point of view. In this work, we have applied the single-shot G0W0 method to a representative set of transition metal oxide perovskites including 3 d (SrTiO3, LaScO3, SrMnO3, LaTiO3, LaVO3, LaCrO3, LaMnO3, and LaFeO3), 4 d (SrZrO3, SrTcO3, and Ca2RuO4 ), and 5 d (SrHfO3, KTaO3, and NaOsO3) compounds with different electronic configurations, magnetic orderings, structural characteristics, and band gaps ranging from 0.1 to 6.1 eV. We discuss the proper procedure to obtain well-converged QP energies and accurate band gaps within single-shot G0W0 by comparing the conventional approach based on an incremental variation of a specific set of parameters (number of bands, energy cutoff for the plane-wave expansion and number of k points) and the basis-set extrapolation scheme [J. Klimeš et al., Phys. Rev. B 90, 075125 (2014), 10.1103/PhysRevB.90.075125]. Although the conventional scheme is not supported by a formal proof of convergence, for most cases it delivers QP energies in reasonably good agreement with those obtained by the basis-set correction procedure and it is by construction more useful for calculating band structures. In addition, we have inspected the difference between the adoption of norm-conserving and ultrasoft potentials in G W calculations and found that the norm violation for the d shell can lead to less accurate results in particular for charge-transfer systems and late transition metals. A minimal statistical analysis indicates that the correlation of the G W data

Spin currents in metallic nanostructures

Energy Technology Data Exchange (ETDEWEB)

Czeschka, Franz Dominik

2011-09-05

A pure spin current, i.e., a flow of angular momentum without accompanying net charge current, is a key ingredient in the field of spintronics. In this thesis, we experimentally investigated two different concepts for pure spin current sources suggested by theory. The first is based on a time-dependent magnetization precession which ''pumps'' a pure spin current into an adjacent non-magnetic conductor. Our experiments quantitatively corroborated important predictions expected theoretically for this approach, including the dependence of the spin current on the sample geometry and the microwave power. Even more important, we could show for the first time that the spin pumping concept is viable in a large variety of ferromagnetic materials and that it only depends on the magnetization damping. Therefore, our experiments established spin pumping as generic phenomenon and demonstrated that it is a powerful way to generate pure spin currents. The second theoretical concept is based on the conversion of charge currents into spin currents in non-magnetic nanostructures via the spin Hall effect. We experimentally investigated this approach in H-shaped, metallic nanodevices, and found that the predictions are linked to requirements not realizable with the present experimental techniques, neither in sample fabrication nor in measurement technique. Indeed, our experimental data could be consistently understood by a spin-independent transport model describing the transition from diffusive to ballistic transport. In addition, the implementation of advanced fabrication and measurement techniques allowed to discover a new non-local phenomenon, the non-local anisotropic magnetoresistance. Finally, we also studied spin-polarized supercurrents carried by spin-triplet Cooper pairs. We found that low resistance interfaces are a key requirement for further experiments in this direction. (orig.)

Giant magnetoresistance effect in nanostructures consisting of magnetic-electric barriers

International Nuclear Information System (INIS)

Tang, Wei-Hua; Li, Chun-Shu; Kong, Yong-Hong; Zhang, Gui-Lian

2007-01-01

The GMR effect in magnetic-electric barrier nanostructure, which can be realized experimentally by depositing two parallel metallic ferromagnetic strips with an applied voltage on the top of heterostructure, is investigated theoretically. It is shown that a considerable GMR effect can be achieved in such nanosystems due to the significant transmission difference for electrons tunneling through parallel and antiparallel magnetization configurations. It is also shown that the magnetoresistance ratio is strongly dependent upon the applied voltage to metallic ferromagnetic strips in nanosystems, thus may leading to voltage-tunable GMR devices

Spontaneous magnetization of thin films of ordered and disordered alloys of transition metals

International Nuclear Information System (INIS)

Nguyen Nhat Khanh.

1989-12-01

A method of calculation of spontaneous magnetization of thin films of transition metal alloys is described. The method is based on the Hubbard model for d electrons. Use of the Bragg-Williams approximation and two-dimensional canonical transformations has allowed to calculate the magnetization. Results for a Ni 3 Fe thin film are presented. (author). 11 refs, 1 fig

Metal nanostructures: from clusters to nanocatalysis and sensors

Science.gov (United States)

Smirnov, B. M.

2017-12-01

The properties of metal clusters and nanostructures composed of them are reviewed. Various existing methods for the generation of intense beams of metal clusters and their subsequent conversion into nanostructures are compared. Processes of the flow of a buffer gas with active molecules through a nanostructure are analyzed as a basis of using nanostructures for catalytic applications. The propagation of an electric signal through a nanostructure is studied by analogy with a macroscopic metal. An analysis is given of how a nanostructure changes its resistance as active molecules attach to its surface and are converted into negative ions. These negative ions induce the formation of positively charged vacancies inside the metal conductor and attract the vacancies to together change the resistance of the metal nanostructure. The physical basis is considered for using metal clusters and nanostructures composed of them to create new materials in the form of a porous metal film on the surface of an object. The fundamentals of nanocatalysis are reviewed. Semiconductor conductometric sensors consisting of bound nanoscale grains or fibers acting as a conductor are compared with metal sensors conducting via a percolation cluster, a fractal fiber, or a bunch of interwoven nanofibers formed in superfluid helium. It is shown that sensors on the basis of metal nanostructures are characterized by a higher sensitivity than semiconductor ones, but are not selective. Measurements using metal sensors involve two stages, one of which measures to high precision the attachment rate of active molecules to the sensor conductor, and in the other one the surface of metal nanostructures is cleaned from the attached molecules using a gas discharge plasma (in particular, capillary discharge) with a subsequent chromatography analysis for products of cleaning.

VUV photo-oxidation of gaseous benzene combined with ozone-assisted catalytic oxidation: Effect on transition metal catalyst

International Nuclear Information System (INIS)

Huang, Haibao; Lu, Haoxian; Zhan, Yujie; Liu, Gaoyuan; Feng, Qiuyu; Huang, Huiling; Wu, Muyan; Ye, Xinguo

2017-01-01

Graphical abstract: Mn nanoparticles are highly dispersed on ZSM-5 and most efficient in benzene degradation in the VUV-OZCO process. - Highlights: • Vacuum UV irradiation is well combined with O_3 catalytic oxidation. • O_3 byproducts was used to enhance catalytic oxidation of VOCs. • Mn/ZSM-5 achieved the best catalytic activity for benzene degradation. - Abstract: Volatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O_3, the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O_3 catalytic decomposition and utilization. Benzene and O_3 removal efficiency reached as high as 97% and 100% after 360 min, respectively. O_3 was catalytically decomposed, generating highly reactive oxidants such as ·OH and ·O for benzene oxidation.

VUV photo-oxidation of gaseous benzene combined with ozone-assisted catalytic oxidation: Effect on transition metal catalyst

Energy Technology Data Exchange (ETDEWEB)

Huang, Haibao, E-mail: seabao8@gmail.com [School of Environmental Science and Engineering, Sun Yat-Sen University (China); Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology (Sun Yat-sen University) (China); Lu, Haoxian; Zhan, Yujie; Liu, Gaoyuan; Feng, Qiuyu; Huang, Huiling; Wu, Muyan; Ye, Xinguo [School of Environmental Science and Engineering, Sun Yat-Sen University (China)

2017-01-01

Graphical abstract: Mn nanoparticles are highly dispersed on ZSM-5 and most efficient in benzene degradation in the VUV-OZCO process. - Highlights: • Vacuum UV irradiation is well combined with O{sub 3} catalytic oxidation. • O{sub 3} byproducts was used to enhance catalytic oxidation of VOCs. • Mn/ZSM-5 achieved the best catalytic activity for benzene degradation. - Abstract: Volatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O{sub 3}, the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O{sub 3} catalytic decomposition and utilization. Benzene and O{sub 3} removal efficiency reached as high as 97% and 100% after 360 min, respectively. O{sub 3} was catalytically decomposed, generating highly reactive oxidants such as ·OH and ·O for benzene oxidation.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †.

Science.gov (United States)

Afzal, Adeel; Dickert, Franz L

2018-04-20

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

Photoelectrochemical properties and band structure of oxide films on zirconium-transition metal alloys

International Nuclear Information System (INIS)

Takahashi, Kazuo; Uno, Masayoshi; Okui, Mihoko; Yamanaka, Shinsuke

2006-01-01

The microalloying effects of 4d and 5d transition metals, M (M: Nb, Mo, Ta, W) on the photoelectrochemical properties, the flat band potential (U fb ) and the band gap energy (E g ), for zirconium oxide films were investigated by photoelectrochemical measurements and band calculation. Button ingots of zirconium-5 mol% M (M: Nb, Mo, Ta, W) were made from high-purity metals (99.9% purity) by arc melting in a purified argon atmosphere. These plate specimens were sealed into silica tubes in vacuum, and then homogenized at 1273 K for 24 h. Subsequently, these specimens were oxidized up to 1173 K. The photocurrent of each specimen was evaluated at room temperature under the irradiation of Xe lamp (500 W) through grating monochrometer and cut-off filter. 0.1 M Na 2 SO 4 solution was used as the electrolyte. The value of the flat band potential was higher and the value of the band gap energy was smaller than that of pure zirconium oxide film in all sample. It was found from the calculation by CASTEP code that the decreases in band gap energy of these oxide films was due to formation of 4d or 5d orbital of transition metals

Commercial Implementation of Model-Based Manufacturing of Nanostructured Metals

Energy Technology Data Exchange (ETDEWEB)

Lowe, Terry C. [Los Alamos National Laboratory

2012-07-24

Computational modeling is an essential tool for commercial production of nanostructured metals. Strength is limited by imperfections at the high strength levels that are achievable in nanostructured metals. Processing to achieve homogeneity at the micro- and nano-scales is critical. Manufacturing of nanostructured metals is intrinsically a multi-scale problem. Manufacturing of nanostructured metal products requires computer control, monitoring and modeling. Large scale manufacturing of bulk nanostructured metals by Severe Plastic Deformation is a multi-scale problem. Computational modeling at all scales is essential. Multiple scales of modeling must be integrated to predict and control nanostructural, microstructural, macrostructural product characteristics and production processes.

Characterization of Transition Metal Oxide/Silicon Heterojunctions for Solar Cell Applications

Directory of Open Access Journals (Sweden)

Luis G. Gerling

2015-10-01

Full Text Available During the last decade, transition metal oxides have been actively investigated as hole- and electron-selective materials in organic electronics due to their low-cost processing. In this study, four transition metal oxides (V2O5, MoO3, WO3, and ReO3 with high work functions (>5 eV were thermally evaporated as front p-type contacts in planar n-type crystalline silicon heterojunction solar cells. The concentration of oxygen vacancies in MoO3−x was found to be dependent on film thickness and redox conditions, as determined by X-ray Photoelectron Spectroscopy. Transfer length method measurements of oxide films deposited on glass yielded high sheet resistances (~109 Ω/sq, although lower values (~104 Ω/sq were measured for oxides deposited on silicon, indicating the presence of an inversion (hole rich layer. Of the four oxide/silicon solar cells, ReO3 was found to be unstable upon air exposure, while V2O5 achieved the highest open-circuit voltage (593 mV and conversion efficiency (12.7%, followed by MoO3 (581 mV, 12.6% and WO3 (570 mV, 11.8%. A short-circuit current gain of ~0.5 mA/cm2 was obtained when compared to a reference amorphous silicon contact, as expected from a wider energy bandgap. Overall, these results support the viability of a simplified solar cell design, processed at low temperature and without dopants.

Magnetic nanostructures: radioactive probes and recent developments

International Nuclear Information System (INIS)

Prandolini, M J

2006-01-01

The miniaturization of magnetic sensors and storage devices down to the nano-scale leads to drastic changes in magnetic phenomena compared with the same devices with a larger size. Excited-nuclear-probe (radioactive probe) techniques are ideal for investigating these new magnetic nanostructures. By observing the magnetic hyperfine fields (and in some cases the electric-field-gradients (EFGs)) at the nuclei of radioactive probes, microscopic information about the magnetic environment of the probes is acquired. The magnetic hyperfine field is particularly sensitive to the s-spin polarization of the conduction electrons and to the orbital magnetic moment of the probe atom. Three methods of inserting radioactive probes into magnetic nanostructures are presented; neutron activation, recoil implantation and 'soft-landing', followed by descriptions of their application to selected examples. In some cases, these methods offer the simultaneous creation and observation of new magnetic materials at the atomic scale. This review focuses firstly on the induced magnetism in noble-metal spacer layers between either ferromagnetic (FM) or FM/antiferromagnetic (AFM) layers in a trilayer structure. Using the method of low-temperature nuclear orientation, the s-spin polarization of noble-metal probes was measured and was found to be very sensitive to the magnetic properties at both the FM and AFM interfaces. Secondly, the recoil implantation of radioactive Fe probes into rare-earth hosts and d-band alloys and subsequent measurement using time-differential perturbed angular distribution offer the possibility of controlling the chemical composition and number of nearest-neighbours. This method was used to prepare local 3d-magnetic clusters in a non-magnetic matrix and to observe their magnetic behaviour. Finally, non-magnetic radioactive probes were 'soft-landed' onto Ni surfaces and extremely lattice-expanded ultrathin Ni films. By measuring the magnetic hyperfine fields and EFGs at

Quantitative chemical state XPS analysis of first row transition metals, oxides and hydroxides

International Nuclear Information System (INIS)

Biesinger, M C; Payne, B P; McIntryre, N S; Hart, B R; Lau, L Wm; Grosvenor, A P; Smart, R StC

2008-01-01

Practical quantitative chemical state X-ray photoelectron spectroscopy (XPS) analysis of first row transition metals, oxides and hydroxides is challenging due to the complexity of their M 2p spectra. Complex multiplet splitting, shake-up and plasmon loss structure can play a role in the interpretation of the chemical states present. This paper will show practical curve fitting procedures for the quantitative measurement of different chemical states for metal oxides and hydroxides from a survey of transition metals. It will also discuss some of the limitations and pitfalls present as well as give practical examples of their successful use. These curve-fitting procedures are based on 1) standard spectra from quality reference samples, 2) a survey of appropriate literature databases and/or a compilation of literature references, 3) fitting of multiplet split spectra based on spectra of numerous reference materials and theoretical modelling, 4) spectral subtractions routines, again using reference spectra, and 5) specific literature references where fitting procedures are available

Quantitative chemical state XPS analysis of first row transition metals, oxides and hydroxides

Energy Technology Data Exchange (ETDEWEB)

Biesinger, M C; Payne, B P; McIntryre, N S [Department of Chemistry, University of Western Ontario, London, Ontario, N6A 5B7 (Canada); Hart, B R; Lau, L Wm [Surface Science Western, Room G1, Western Science Centre, University of Western Ontario, London, Ontario, N6A 5B7 (Canada); Grosvenor, A P [Department of Chemistry, Gunning/Lemieux Chemistry Centre, University of Alberta, Edmonton, Alberta, T6G 2G2 (Canada); Smart, R StC [ACeSSS, Applied Centre for Structural and Synchrotron Studies, University of South Australia, Mawson Lakes, SA 5095 (Australia)], E-mail: biesingr@uwo.ca

2008-03-15

Practical quantitative chemical state X-ray photoelectron spectroscopy (XPS) analysis of first row transition metals, oxides and hydroxides is challenging due to the complexity of their M 2p spectra. Complex multiplet splitting, shake-up and plasmon loss structure can play a role in the interpretation of the chemical states present. This paper will show practical curve fitting procedures for the quantitative measurement of different chemical states for metal oxides and hydroxides from a survey of transition metals. It will also discuss some of the limitations and pitfalls present as well as give practical examples of their successful use. These curve-fitting procedures are based on 1) standard spectra from quality reference samples, 2) a survey of appropriate literature databases and/or a compilation of literature references, 3) fitting of multiplet split spectra based on spectra of numerous reference materials and theoretical modelling, 4) spectral subtractions routines, again using reference spectra, and 5) specific literature references where fitting procedures are available.

Ab initio investigations of magnetic properties of ultrathin transition-metal films on 4d substrates

Energy Technology Data Exchange (ETDEWEB)

Al-Zubi, Ali

2010-12-22

In this thesis, we investigate the magnetic properties of 3d transition-metal monolayers on 4d transition-metal substrates by means of state of the art first-principles quantum theory. In order to reveal the underlying physics of these systems we study trends by performing systematic investigations across the transition-metal series. Case studies are presented for which Rh has been chosen as exemplary 4d substrate. We consider two substrate orientations, a square lattice provided by Rh(001) and a hexagonal lattice provided by Rh(111). We find, all 3d transition-metal (V, Cr, Mn, Fe, Co and Ni) monolayers deposited on the Rh substrate are magnetic and exhibit large local moments which follow Hund's rule with a maximum magnetic moment for Mn of about 3.7 {mu}{sub B} depending on the substrate orientation. The largest induced magnetic moment of about 0.46 {mu}{sub B} is found for Rh atoms adjacent to the Co(001)-film. On Rh(001) we predict a ferromagnetic (FM) ground state for V, Co and Ni, while Cr, Mn and Fe monolayers favor a c(2 x 2) antiferromagnetic (AFM) state, a checkerboard arrangement of up and down magnetic moments. The magnetic anisotropy energies of these ultrathin magnetic films are calculated for the FM and the AFM states. With the exception of V and Cr, the easy axis of the magnetization is predicted to be in the film plane. With the exception of Fe, analogous results are obtained for the 3d-metal monolayers on Rh(111). For Fe on Rh(111) a novel magnetic ground state is predicted, a double-row-wise antiferromagnetic state along the [11 anti 2] direction, a sequence of ferromagnetic double-rows of atoms, whose magnetic moments couple antiferromagnetically from double row to double row. The magnetic structure can be understood as superposition of a left- and right-rotating flat spin spiral. In a second set of case studies the properties of an Fe monolayer deposited on varies hexagonally terminated hcp (0001) and fcc (111) surfaces of 4d-transition

Ab initio investigations of magnetic properties of ultrathin transition-metal films on 4d substrates

International Nuclear Information System (INIS)

Al-Zubi, Ali

2010-01-01

In this thesis, we investigate the magnetic properties of 3d transition-metal monolayers on 4d transition-metal substrates by means of state of the art first-principles quantum theory. In order to reveal the underlying physics of these systems we study trends by performing systematic investigations across the transition-metal series. Case studies are presented for which Rh has been chosen as exemplary 4d substrate. We consider two substrate orientations, a square lattice provided by Rh(001) and a hexagonal lattice provided by Rh(111). We find, all 3d transition-metal (V, Cr, Mn, Fe, Co and Ni) monolayers deposited on the Rh substrate are magnetic and exhibit large local moments which follow Hund's rule with a maximum magnetic moment for Mn of about 3.7 μ B depending on the substrate orientation. The largest induced magnetic moment of about 0.46 μ B is found for Rh atoms adjacent to the Co(001)-film. On Rh(001) we predict a ferromagnetic (FM) ground state for V, Co and Ni, while Cr, Mn and Fe monolayers favor a c(2 x 2) antiferromagnetic (AFM) state, a checkerboard arrangement of up and down magnetic moments. The magnetic anisotropy energies of these ultrathin magnetic films are calculated for the FM and the AFM states. With the exception of V and Cr, the easy axis of the magnetization is predicted to be in the film plane. With the exception of Fe, analogous results are obtained for the 3d-metal monolayers on Rh(111). For Fe on Rh(111) a novel magnetic ground state is predicted, a double-row-wise antiferromagnetic state along the [11 anti 2] direction, a sequence of ferromagnetic double-rows of atoms, whose magnetic moments couple antiferromagnetically from double row to double row. The magnetic structure can be understood as superposition of a left- and right-rotating flat spin spiral. In a second set of case studies the properties of an Fe monolayer deposited on varies hexagonally terminated hcp (0001) and fcc (111) surfaces of 4d-transition metals (Tc, Ru, Rh

Ab initio investigations of magnetic properties of ultrathin transition-metal films on 4d substrates

Energy Technology Data Exchange (ETDEWEB)

Al-Zubi, Ali

2010-12-22

In this thesis, we investigate the magnetic properties of 3d transition-metal monolayers on 4d transition-metal substrates by means of state of the art first-principles quantum theory. In order to reveal the underlying physics of these systems we study trends by performing systematic investigations across the transition-metal series. Case studies are presented for which Rh has been chosen as exemplary 4d substrate. We consider two substrate orientations, a square lattice provided by Rh(001) and a hexagonal lattice provided by Rh(111). We find, all 3d transition-metal (V, Cr, Mn, Fe, Co and Ni) monolayers deposited on the Rh substrate are magnetic and exhibit large local moments which follow Hund's rule with a maximum magnetic moment for Mn of about 3.7 {mu}{sub B} depending on the substrate orientation. The largest induced magnetic moment of about 0.46 {mu}{sub B} is found for Rh atoms adjacent to the Co(001)-film. On Rh(001) we predict a ferromagnetic (FM) ground state for V, Co and Ni, while Cr, Mn and Fe monolayers favor a c(2 x 2) antiferromagnetic (AFM) state, a checkerboard arrangement of up and down magnetic moments. The magnetic anisotropy energies of these ultrathin magnetic films are calculated for the FM and the AFM states. With the exception of V and Cr, the easy axis of the magnetization is predicted to be in the film plane. With the exception of Fe, analogous results are obtained for the 3d-metal monolayers on Rh(111). For Fe on Rh(111) a novel magnetic ground state is predicted, a double-row-wise antiferromagnetic state along the [11 anti 2] direction, a sequence of ferromagnetic double-rows of atoms, whose magnetic moments couple antiferromagnetically from double row to double row. The magnetic structure can be understood as superposition of a left- and right-rotating flat spin spiral. In a second set of case studies the properties of an Fe monolayer deposited on varies hexagonally terminated hcp (0001) and fcc (111) surfaces of 4d-transition metals

Characterization of Transition-Metal Oxide Deposition on Carbon Electrodes of a Supercapacitor

Directory of Open Access Journals (Sweden)

Ying-Chung Chen

2016-12-01

Full Text Available In order to fabricate the composite electrodes of a supercapacitor, transition-metal oxide materials NiO and WO3 were deposited on carbon electrodes by electron beam evaporation. The influences of various transition-metal oxides, scan rates of cyclic voltammograms (CVs, and galvanostatic charge/discharge tests on the characteristics of supercapacitor were studied. The charge/discharge efficiency and the lifetime of the composite electrodes were also investigated. It was found that the composite electrodes exhibited more favorable capacitance properties than those of the carbon electrodes at high scan rates. The results revealed the promotion of the capacitance property of the supercapacitor with composite electrode and the improving of the decay property in capacitance at high scan rate. In addition, the charge/discharge efficiency is close to 100% after 5000 cycles, and the composite electrode retains strong adhesion between the electrode material and the substrate.

Strain tunable magnetic properties of 3d transition-metal ion doped monolayer MoS2: A first-principles study

Science.gov (United States)

Zhu, Yupeng; Liang, Xiao; Qin, Jun; Deng, Longjiang; Bi, Lei

2018-05-01

In this article, a systematic study on the magnetic properties and strain tunability of 3d transition metal ions (Mn, Fe, Co, Ni) doped MoS2 using first-principles calculations is performed. Antiferromagnetic coupling is observed between Mn, Fe ions and the nearest neighbor Mo ions; whereas ferromagnetic coupling is observed in Co and Ni systems. It is also shown that by applying biaxial tensile strain, a significant change of the magnetic moment is observed in all transition metal doped MoS2 materials with a strain threshold. The changes of total magnetic moment have different mechanisms for different doping systems including an abrupt change of the bond lengths, charge transfer and strain induced structural anisotropy. These results demonstrate applying strain as a promising method for tuning the magnetic properties in transition metal ion doped monolayer MoS2.

Electrochemical oxidation of pulp and paper making wastewater assisted by transition metal modified kaolin

International Nuclear Information System (INIS)

Wang Bo; Gu Lin; Ma Hongzhu

2007-01-01

The electrochemical oxidation of pulp and paper making wastewater assisted by transition metal (Co, Cu) modified kaolin in a 200 ml electrolytic batch reactor with graphite plate as electrodes was investigated. H 2 O 2 , which produced on the surface of porous graphite cathode, would react with the catalysts to form strong oxidant (hydroxyl radicals) that can in turn destruct the pollutants adsorbed on the surface of kaolin. The transition metal (Co, Cu) modified kaolin was also characterized by XRD and SEM before and after the modification and the results showed that the transition metals were completely supported on kaolin and formed a porous structure with big BET surface. The mechanism was proposed on the basis of XPS analysis of the catalyst after the degradation process. Series of experiments were also done to prove the synergetic effect of the combined oxidation system and to find out the optimal operating parameters such as initial pH, current density and amount of catalyst. From the results it can be founded that when the initial pH was at 3, current density was 30 mA cm -2 ; catalyst dose was 30 g dm -3 , COD (chemical oxygen demand) removal could reach up to 96.8% in 73 min

Chemically synthesized metal-oxide-metal segmented nanowires with high ferroelectric response

Energy Technology Data Exchange (ETDEWEB)

Herderick, Edward D; Padture, Nitin P [Department of Materials Science and Engineering, Center for Emergent Materials, Ohio State University, Columbus, OH 43210 (United States); Polomoff, Nicholas A; Huey, Bryan D, E-mail: padture.1@osu.edu [Department of Chemical, Materials, and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, CT 06269 (United States)

2010-08-20

A chemical synthesis method is presented for the fabrication of high-definition segmented metal-oxide-metal (MOM) nanowires in two different ferroelectric oxide systems: Au-BaTiO{sub 3}-Au and Au-PbTiO{sub 3}-Au. This method entails electrodeposition of segmented nanowires of Au-TiO{sub 2}-Au inside anodic aluminum oxide (AAO) templates, followed by topotactic hydrothermal conversion of the TiO{sub 2} segments into BaTiO{sub 3} or PbTiO{sub 3} segments. Two-terminal devices from individual MOM nanowires are fabricated, and their ferroelectric properties are measured directly, without the aid of scanning probe microscopy (SPM) methods. The MOM nanowire architecture provides high-quality end-on electrical contacts to the oxide segments, and allows direct measurement of properties of nanoscale volume, strain-free oxide segments. Unusually high ferroelectric responses, for chemically synthesized oxides, in these MOM nanowires are reported, and are attributed to the lack of residual strain in the oxides. The ability to measure directly the active properties of nanoscale volume, strain-free oxides afforded by the MOM nanowire architecture has important implications for fundamental studies of not only ferroelectric nanostructures but also nanostructures in the emerging field of multiferroics.

Enhancement of chitosan-graphene oxide SPR sensor with a multi-metallic layers of Au–Ag–Au nanostructure for lead(II) ion detection

Energy Technology Data Exchange (ETDEWEB)

Kamaruddin, Nur Hasiba [Department of Electric, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Bakar, Ahmad Ashrif A., E-mail: ashrif@ukm.edu.my [Department of Electric, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Yaacob, Mohd Hanif; Mahdi, Mohd Adzir [Wireless and Photonic Network Research Centre, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Selangor (Malaysia); Zan, Mohd Saiful Dzulkefly [Department of Electric, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia); Shaari, Sahbudin [Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor (Malaysia)

2016-01-15

Highlights: • Tri-metallic Au–Ag–Au CS-GO SPR sensor was fabricated for the first time. • The tri-metallic nanostructure provided an enhanced evanescent field. • Successful functionalization of the CS-GO sensing layer. • Superior performance for lead(II) ion detection. - Abstract: We demonstrate the enhancement of surface plasmon resonance (SPR) technique by implementing a multi-metallic layers of Au–Ag–Au nanostructure in the chitosan-graphene oxide (CS-GO) SPR sensor for lead(II) ion detection. The performance of the sensor is analyzed via SPR measurements, from which the sensitivity, signal-to-noise ratio and repeatability are determined. The nanostructure layers are characterized using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). We showed that the proposed structure has increased the shift in the SPR angle up to 3.5° within the range of 0.1–1 ppm due to the enhanced evanescent field at the sensing layer-analyte interface. This sensor also exhibits great repeatability which benefits from the stable multi-metallic nanostructure. The SNR value of 0.92 for 5 ppm lead(II) ion solution and reasonable linearity range up to that concentration shows that the tri-metallic CS-GO SPR sensor gives a good response towards the lead(II) ion solution. The CS-GO SPR sensor is also sensitive to at least a 10{sup −5} change in the refractive index. The results prove that our proposed tri-metallic CS-GO SPR sensor demonstrates a strong performance and reliability for lead(II) ion detection in accordance with the standardized lead safety level for wastewater.

Empirical correction for PM7 band gaps of transition-metal oxides.

Science.gov (United States)

Liu, Xiang; Sohlberg, Karl

2016-01-01

A post-calculation correction is established for PM7 band gaps of transition-metal oxides. The correction is based on the charge on the metal cation of interest, as obtained from MOPAC PM7 calculations. Application of the correction reduces the average error in the PM7 band gap from ~3 eV to ~1 eV. The residual error after correction is shown to be uncorrelated to the Hartree-Fock method upon which PM7 is based. Graphical Abstract Comparison between calculated band gaps and experimental band gaps for binary oxides. The orange crosses are for corrected PM7 band gaps. Blue squares are uncorrected values. The orange crosses fall closer to the diagonal dashed line, showing an overall improvement of the accuracy of calculated values.

GREENER PRODUCTION OF NOBLE METAL NANOSTRUCTURES AND NANOCOMPOSITES: RISK REDUCTION AND APPLICATIONS

Science.gov (United States)

The synthesis of nanometal/nano metal oxide/nanostructured polymer and their stabilization (through dispersant, biodegradable polymer) involves the use of natural renewable resources such plant material extract, biodegradable polymers, sugars, vitamins and finally efficient and s...

Modification of implant material surface properties by means of oxide nano-structured coatings deposition

Science.gov (United States)

Safonov, Vladimir; Zykova, Anna; Smolik, Jerzy; Rogowska, Renata; Lukyanchenko, Vladimir; Kolesnikov, Dmitrii

2014-08-01

The deposition of functional coatings on the metal surface of artificial joints is an effective way of enhancing joint tribological characteristics. It is well-known that nanostructured oxide coatings have specific properties advantageous for future implant applications. In the present study, we measured the high hardness parameters, the adhesion strength and the low friction coefficient of the oxide magnetron sputtered coatings. The corrosion test results show that the oxide coating deposition had improved the corrosion resistance by a factor of ten for both stainless steel and titanium alloy substrates. Moreover, the hydrophilic nature of coated surfaces in comparison with the metal ones was investigated in the tensiometric tests. The surfaces with nanostructured oxide coatings demonstrated improved biocompatibility for in vitro and in vivo tests, attributed to the high dielectric constants and the high values of the surface free energy parameters.

Electronic and magnetic properties of 1T-HfS{sub 2} by doping transition-metal atoms

Energy Technology Data Exchange (ETDEWEB)

Zhao, Xu, E-mail: zhaoxu@htu.cn [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Wang, Tianxing; Wang, Guangtao [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Dai, Xianqi [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Department of Physics, Zhengzhou Normal University, Zhengzhou, Henan 450044 (China); Xia, Congxin [College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, Henan 453007 (China); Yang, Lin [School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang 453007 (China)

2016-10-15

Highlights: • Pristine 1T-HfS{sub 2} is a semiconductor with indirect gaps of 1.250 eV • Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. • Strong p–d hybridization was found between TM 3d orbitals and S 3p orbitals. • V-doped 1T-HfS{sub 2} is ideal for spin injection. - Abstract: We explored the electronic and magnetic properties of 1T-HfS{sub 2} doped by transition metal (TM) atom using the first-principles calculation. We doped the transition metal atoms from the IIIB to VIB groups in nonmagnetic 1T-HfS{sub 2}. Numerical results show that the pristine 1T-HfS{sub 2} is a semiconductor with indirect gaps of 1.250 eV. Magnetism can be observed for V, Cr, Mn, Fe, Co, and Cu doping. The polarized charges mainly arise from the localized 3d electrons of the TM atom. The strong p–d hybridization was found between the 3d orbitals of TM and 3p orbitals of S. The substituted 1T-HfS{sub 2} can be a metal, semiconductor or half-metal. Analysis of the band structure and magnetic properties indicates that TM-doped HfS{sub 2} (TM = V, Fe, Cu) are promising systems to explore two-dimensional diluted magnetic semiconductors. The formation energy calculations also indicate that it is energetically favorable and relatively easier to incorporate transition metal atom into the HfS{sub 2} under S-rich experimental conditions. In contrast, V-doped HfS{sub 2} has relatively wide half-metallic gap and low formation energy. So V-doped 1T-HfS{sub 2} is ideal for spin injection, which is important for application in semiconductor spintronics.

Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

DEFF Research Database (Denmark)

Tritsaris, G. A.; Rossmeisl, J.

2012-01-01

Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, flat...... sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....

Optimization of film synthesized rare earth transition metal permanent magnet systems

International Nuclear Information System (INIS)

Cadieu, F.J.

1992-01-01

Progress is reported in three areas: high coercivity Sm-Fe-Ti-V, Sm-Fe-Zr, and two element Sm-Fe Sm 5 (Fe,T) 17 type crystalline phases; ThMn 12 type pseudobinary SmFe 12-x T x (0≤x≤1.5); and sputter process control for the synthesis of precisely textured rare earth-transition metal magnetic films

Mesoporous metal oxides and processes for preparation thereof

Energy Technology Data Exchange (ETDEWEB)

Suib, Steven L.; Poyraz, Altug Suleyman

2018-03-06

A process for preparing a mesoporous metal oxide, i.e., transition metal oxide. Lanthanide metal oxide, a post-transition metal oxide and metalloid oxide. The process comprises providing an acidic mixture comprising a metal precursor, an interface modifier, a hydrotropic ion precursor, and a surfactant; and heating the acidic mixture at a temperature and for a period of time sufficient to form the mesoporous metal oxide. A mesoporous metal oxide prepared by the above process. A method of controlling nano-sized wall crystallinity and mesoporosity in mesoporous metal oxides. The method comprises providing an acidic mixture comprising a metal precursor, an interface modifier, a hydrotropic ion precursor, and a surfactant; and heating the acidic mixture at a temperature and for a period of time sufficient to control nano-sized wall crystallinity and mesoporosity in the mesoporous metal oxides. Mesoporous metal oxides and a method of tuning structural properties of mesoporous metal oxides.

Calcium-assisted reduction of cobalt ferrite nanoparticles for nanostructured iron cobalt with enhanced magnetic performance

International Nuclear Information System (INIS)

Qi, B.; Andrew, J. S.; Arnold, D. P.

2017-01-01

This paper demonstrates the potential of a calcium-assisted reduction process for synthesizing fine-grain (~100 nm) metal alloys from metal oxide nanoparticles. To demonstrate the process, an iron cobalt alloy (Fe_6_6Co_3_4) is obtained by hydrogen annealing 7-nm cobalt ferrite (CoFe_2O_4) nanoparticles in the presence of calcium granules. The calcium serves as a strong reducing agent, promoting the phase transition from cobalt ferrite to a metallic iron cobalt alloy, while maintaining high crystallinity. Magnetic measurements demonstrate the annealing temperature is the dominant factor of tuning the grain size and magnetic properties. Annealing at 700 °C for 1 h maximizes the magnetic saturation, up to 2.4 T (235 emu/g), which matches that of bulk iron cobalt.

Calcium-assisted reduction of cobalt ferrite nanoparticles for nanostructured iron cobalt with enhanced magnetic performance

Energy Technology Data Exchange (ETDEWEB)

Qi, B. [University of Florida, Interdisciplinary Microsystems Group, Department of Electrical and Computer Engineering (United States); Andrew, J. S. [University of Florida, Department of Materials Science and Engineering (United States); Arnold, D. P., E-mail: darnold@ufl.edu [University of Florida, Interdisciplinary Microsystems Group, Department of Electrical and Computer Engineering (United States)

2017-03-15

This paper demonstrates the potential of a calcium-assisted reduction process for synthesizing fine-grain (~100 nm) metal alloys from metal oxide nanoparticles. To demonstrate the process, an iron cobalt alloy (Fe{sub 66}Co{sub 34}) is obtained by hydrogen annealing 7-nm cobalt ferrite (CoFe{sub 2}O{sub 4}) nanoparticles in the presence of calcium granules. The calcium serves as a strong reducing agent, promoting the phase transition from cobalt ferrite to a metallic iron cobalt alloy, while maintaining high crystallinity. Magnetic measurements demonstrate the annealing temperature is the dominant factor of tuning the grain size and magnetic properties. Annealing at 700 °C for 1 h maximizes the magnetic saturation, up to 2.4 T (235 emu/g), which matches that of bulk iron cobalt.

Metal chalcogenide nanostructures for renewable energy applications

CERN Document Server

Qurashi, Ahsanulhaq

2014-01-01

This first ever reference book that focuses on metal chalcogenide semiconductor nanostructures for renewable energy applications encapsulates the state-of-the-art in multidisciplinary research on the metal chalcogenide semiconductor nanostructures (nanocrystals, nanoparticles, nanorods, nanowires,  nanobelts, nanoflowers, nanoribbons and more).  The properties and synthesis of a class of nanomaterials is essential to renewable energy manufacturing and this book focuses on the synthesis of metal chalcogendie nanostructures, their growth mechanism, optical, electrical, and other important prop

Molecular water oxidation mechanisms followed by transition metals: state of the art.

Science.gov (United States)

Sala, Xavier; Maji, Somnath; Bofill, Roger; García-Antón, Jordi; Escriche, Lluís; Llobet, Antoni

2014-02-18

One clean alternative to fossil fuels would be to split water using sunlight. However, to achieve this goal, researchers still need to fully understand and control several key chemical reactions. One of them is the catalytic oxidation of water to molecular oxygen, which also occurs at the oxygen evolving center of photosystem II in green plants and algae. Despite its importance for biology and renewable energy, the mechanism of this reaction is not fully understood. Transition metal water oxidation catalysts in homogeneous media offer a superb platform for researchers to investigate and extract the crucial information to describe the different steps involved in this complex reaction accurately. The mechanistic information extracted at a molecular level allows researchers to understand both the factors that govern this reaction and the ones that derail the system to cause decomposition. As a result, rugged and efficient water oxidation catalysts with potential technological applications can be developed. In this Account, we discuss the current mechanistic understanding of the water oxidation reaction catalyzed by transition metals in the homogeneous phase, based on work developed in our laboratories and complemented by research from other groups. Rather than reviewing all of the catalysts described to date, we focus systematically on the several key elements and their rationale from molecules studied in homogeneous media. We organize these catalysts based on how the crucial oxygen-oxygen bond step takes place, whether via a water nucleophilic attack or via the interaction of two M-O units, rather than based on the nuclearity of the water oxidation catalysts. Furthermore we have used DFT methodology to characterize key intermediates and transition states. The combination of both theory and experiments has allowed us to get a complete view of the water oxidation cycle for the different catalysts studied. Finally, we also describe the various deactivation pathways for

Predicted stability, structures, and magnetism of 3d transition metal nitrides: the M4N phases

NARCIS (Netherlands)

Fang, C.M.; Koster, R.S.; Li, W.F.; van Huis, M.A.

2014-01-01

The 3d transition metal nitrides M4N (Sc4N, Ti4N, V4N, Cr4N, Mn4N, Fe4N, Co4N, Ni4N, and Cu4N) have unique phase relationships, crystal structures, and electronic and magnetic properties. Here we present a systematic density functional theory (DFT) study on these transition metal nitrides, assessing

Metal oxide nanosensors using polymeric membranes, enzymes and antibody receptors as ion and molecular recognition elements.

Science.gov (United States)

Willander, Magnus; Khun, Kimleang; Ibupoto, Zafar Hussain

2014-05-16

The concept of recognition and biofunctionality has attracted increasing interest in the fields of chemistry and material sciences. Advances in the field of nanotechnology for the synthesis of desired metal oxide nanostructures have provided a solid platform for the integration of nanoelectronic devices. These nanoelectronics-based devices have the ability to recognize molecular species of living organisms, and they have created the possibility for advanced chemical sensing functionalities with low limits of detection in the nanomolar range. In this review, various metal oxides, such as ZnO-, CuO-, and NiO-based nanosensors, are described using different methods (receptors) of functionalization for molecular and ion recognition. These functionalized metal oxide surfaces with a specific receptor involve either a complex formation between the receptor and the analyte or an electrostatic interaction during the chemical sensing of analytes. Metal oxide nanostructures are considered revolutionary nanomaterials that have a specific surface for the immobilization of biomolecules with much needed orientation, good conformation and enhanced biological activity which further improve the sensing properties of nanosensors. Metal oxide nanostructures are associated with certain unique optical, electrical and molecular characteristics in addition to unique functionalities and surface charge features which shows attractive platforms for interfacing biorecognition elements with effective transducing properties for signal amplification. There is a great opportunity in the near future for metal oxide nanostructure-based miniaturization and the development of engineering sensor devices.

Oxidation of ethanol on NaX zeolite modified with transition metals

Science.gov (United States)

Mirzai, J. I.; Nadirov, P. A.; Velieva, A. D.; Muradkhanli, V. G.

2017-06-01

NaLaX, NaX + Co, and NaPdX catalysts are synthesized by modification of NaX zeolite with transition metals (La, Co, Pd). The activity of the prepared materials in catalytic ethanol oxidation is studied in the temperature range of 423-723 K. It is shown that NaPdX and NaX + Co accelerate the reactions of partial and complete oxidation of ethanol as the temperature rises. NaLaX accelerates both intramolecular and intermolecular dehydration of alcohol. It is shown that the NaPdX (1.0% Pd) sample has the highest activity in the complete oxidation of alcohol with the formation of CO2.

Reactive oxygen species-related activities of nano-iron metal and nano-iron oxides.

Science.gov (United States)

Wu, Haohao; Yin, Jun-Jie; Wamer, Wayne G; Zeng, Mingyong; Lo, Y Martin

2014-03-01

Nano-iron metal and nano-iron oxides are among the most widely used engineered and naturally occurring nanostructures, and the increasing incidence of biological exposure to these nanostructures has raised concerns about their biotoxicity. Reactive oxygen species (ROS)-induced oxidative stress is one of the most accepted toxic mechanisms and, in the past decades, considerable efforts have been made to investigate the ROS-related activities of iron nanostructures. In this review, we summarize activities of nano-iron metal and nano-iron oxides in ROS-related redox processes, addressing in detail the known homogeneous and heterogeneous redox mechanisms involved in these processes, intrinsic ROS-related properties of iron nanostructures (chemical composition, particle size, and crystalline phase), and ROS-related bio-microenvironmental factors, including physiological pH and buffers, biogenic reducing agents, and other organic substances. Copyright © 2014. Published by Elsevier B.V.

Magnetic structures synthesized by controlled oxidative etching: Structural characterization and magnetic behavior

Directory of Open Access Journals (Sweden)

Álvaro de Jesús Ruíz-Baltazar

Full Text Available A facile strategy for the fabrication Fe3O4 nanostructures at room temperature and with well-defined morphology is proposed. In this methodology, the iron precursors were reduced by sodium borohydride. Subsequently an oxidative etching process promotes the formation of Fe2O3 nanostructures. Magnetic measurements revealed a well-defined superparamagnetic behavior for the material. The Zero-Field-Cooled (ZFC and Field-Cooled (FC magnetization curves reveals that critical and blocking temperature were 24 and 350 °C respectively. The Fe3O4 nanostructures were characterized using aberration-corrected (Cs scanning transmission electron microscopy (STEM and energy dispersive spectroscopy (EDS. Additionally, Raman spectra support the Fe3O4 presence and corroborate the efficiency of the synthesis process to obtain magnetite. Keywords: Chemical synthesis, Fe3O4 nanoparticles, Structural characterization, Magnetic properties

Raman scattering in transition metal compounds: Titanium and compounds of titanium

Energy Technology Data Exchange (ETDEWEB)

Jimenez, J.; Ederer, D.L.; Shu, T. [Tulane Univ., New Orleans, LA (United States)] [and others

1997-04-01

The transition metal compounds form a very interesting and important set of materials. The diversity arises from the many states of ionization the transition elements may take when forming compounds. This variety provides ample opportunity for a large class of materials to have a vast range of electronic and magnetic properties. The x-ray spectroscopy of the transition elements is especially interesting because they have unfilled d bands that are at the bottom of the conduction band with atomic like structure. This group embarked on the systematic study of transition metal sulfides and oxides. As an example of the type of spectra observed in some of these compounds they have chosen to showcase the L{sub II, III} emission and Raman scattering in some titanium compounds obtained by photon excitation.

Formation of Self-assembled Nanostructure on Noble Metal Islands Based on Anodized Aluminum Oxide

International Nuclear Information System (INIS)

Park, Jong Bae; Kim, Young Sic; Kim, Seong Kyu; Lee, Hae Seong

2004-01-01

We have developed the methodology to produce nanoscale gold rods using an AAO template. Each gold rod was generated in every AAO pore. This nanoislands array of gold formed over the AAO pores can be used as corner stones for building nanostructures. We demonstrated this by forming a nanostructure on the Au/AAO by binding a self-assembly class of molecules onto the metal islands. Anodized aluminum oxide (AAO) has been considered an attractive template for simple fabrication of highly-ordered nanostructures. It provides a 2-dimensional array of hexagonal cells with pores of uniform diameter and inter-pore distance that are adjustable in the range of a few tens to hundreds of nanometers. It can be easily grown on an aluminum sheet with high purity by a sequence of several electrochemical steps; electro-polishing, the 1st anodization, etching, and the 2nd anodization. The pores are grown vertically with respect to the AAO surface. The regularity of the pore structure is usually limited by the inherent grain domain in the aluminum sheet to a few micrometers, but can be improved to cover many millimeters of monodomain by pre-indenting the aluminum sheet with SiC 7 or Si 3 N 4 molds. Although fabrication of such molds requires elaborate and costly processes with e-beam nanolithography, such potentially superb regularity can be practically applied to fabrication of nanoscale devices in electronics, optics, biosensors, etc

Rare-earth metal transition metal borocarbide and nitridoborate superconductors

Energy Technology Data Exchange (ETDEWEB)

Niewa, Rainer; Shlyk, Larysa; Blaschkowski, Bjoern [Stuttgart Univ. (Germany). Inst. fuer Anorganische Chemie

2011-07-01

Few years after the discovery of superconductivity in high-T{sub c} cuprates, borocarbides and shortly after nitridoborates with reasonably high T{sub c}s up to about 23 K attracted considerable attention. Particularly for the rare-earth metal series with composition RNi{sub 2}[B{sub 2}C] it turned out, that several members exhibit superconductivity next to magnetic order with both T{sub c} above or below the magnetic ordering temperature. Therefore, these compounds have been regarded as ideal materials to study the interplay and coexistence of superconductivity and long range magnetic order, due to their comparably high ordering temperatures and similar magnetic and superconducting condensation energies. This review gathers information on the series RNi{sub 2}[B{sub 2}C] and isostructural compounds with different transition metals substituting Ni as well as related series like RM[BC], RM[BN], AM[BN] and R{sub 3}M{sub 2}[BN]{sub 2}N (all with R = rare-earth metal, A = alkaline-earth metal, M = transition metal) with special focus on synthesis, crystal structures and structural trends in correspondence to physical properties. (orig.)

The control of magnetism near metal-to-insulator transitions of VO2 nano-belts

CSIR Research Space (South Africa)

Nkosi, SS

2016-12-01

Full Text Available The magnetic properties of paramagnetic/weakly ferromagnetic films are strongly affected by the proximity to materials that undergo a metal to insulator phase transition. Here, we show that under the deposition conditions associated with structural...

Optical magnetism and plasmonic Fano resonances in metal-insulator-metal oligomers.

Science.gov (United States)

Verre, R; Yang, Z J; Shegai, T; Käll, M

2015-03-11

The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been a subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be realized in plasmonic pentamers constructed from metal-insulator-metal (MIM) sandwich particles. Each MIM unit acts as a magnetic meta-atom and the optical magnetism is rendered quasi-broadband through hybridization of the in-plane modes. We demonstrate that scattering spectra of individual MIM pentamers exhibit multiple Fano resonances and a broad subradiant spectral window that signals the magnetic interaction and a hierarchy of coupling effects in these intricate three-dimensional nanoparticle oligomers.

Nanostructures via DNA scaffold metallization

OpenAIRE

Ning, C.; Zinchenko, A.; Baigl, D.; Pyshkina, O.; Sergeyev, V.; Endo, Kazunaka; Yoshikawa, K.

2005-01-01

The critical role of polymers in process of noble metals nanostructures formation is well known, however, the use of DNA chain template in this process is yet largely unknown. In this study we demonstrate different ways of silver deposition on DNA template and report the influence of silver nanostructures formation on DNA conformational state. Metallization of DNA chain proceeds by two different scenarios depending on DNA conformation. If DNA chain is unfolded (elongated) chain, silver reduct...

A review of cobalt adsorption on transition metal oxides

International Nuclear Information System (INIS)

Walker, S.M.

1987-04-01

This report reviews studies of cobalt adsorption on transition metal oxides, in the context of corrosion product and radioactivity transport in PWR primary circuits. In general, uptake of cobalt increases with pH, with temperature and with decreasing ionic strength. Very little data are available under PWR primary circuit conditions, but the limited data available suggest that cobalt uptake by the zirconium oxide corrosion product layer on fuel pins may be significant compared to that deposited on fuel crud. If fuel crud levels can be reduced in future by coolant chemistry control then uptake by the zirconia will assume a greater relative role. It is planned to use an autoclave to study uptake of cobalt on oxidised Zircaloy surfaces at temperatures up to 593K under PWR primary circuit chemistry conditions. (author)

Metal Oxide Nanosensors Using Polymeric Membranes, Enzymes and Antibody Receptors as Ion and Molecular Recognition Elements

Directory of Open Access Journals (Sweden)

Magnus Willander

2014-05-01

Full Text Available The concept of recognition and biofunctionality has attracted increasing interest in the fields of chemistry and material sciences. Advances in the field of nanotechnology for the synthesis of desired metal oxide nanostructures have provided a solid platform for the integration of nanoelectronic devices. These nanoelectronics-based devices have the ability to recognize molecular species of living organisms, and they have created the possibility for advanced chemical sensing functionalities with low limits of detection in the nanomolar range. In this review, various metal oxides, such as ZnO-, CuO-, and NiO-based nanosensors, are described using different methods (receptors of functionalization for molecular and ion recognition. These functionalized metal oxide surfaces with a specific receptor involve either a complex formation between the receptor and the analyte or an electrostatic interaction during the chemical sensing of analytes. Metal oxide nanostructures are considered revolutionary nanomaterials that have a specific surface for the immobilization of biomolecules with much needed orientation, good conformation and enhanced biological activity which further improve the sensing properties of nanosensors. Metal oxide nanostructures are associated with certain unique optical, electrical and molecular characteristics in addition to unique functionalities and surface charge features which shows attractive platforms for interfacing biorecognition elements with effective transducing properties for signal amplification. There is a great opportunity in the near future for metal oxide nanostructure-based miniaturization and the development of engineering sensor devices.

Correlated effective field theory in transition metal compounds

International Nuclear Information System (INIS)

Mukhopadhyay, Subhasis; Chatterjee, Ibha

2004-01-01

Mean field theory is good enough to study the physical properties at higher temperatures and in higher dimensions. It explains the critical phenomena in a restricted sense. Near the critical temperatures, when fluctuations become important, it may not give the correct results. Similarly in low dimensions, the correlations become important and the mean field theory seems to be inadequate to explain the physical phenomena. At low-temperatures too, the quantum correlations become important and these effects are to be treated in an appropriate way. In 1974, Prof. M.E. Lines of Bell Laboratories, developed a theory which goes beyond the mean field theory and is known as the correlated effective field (CEF) theory. It takes into account the fluctuations in a semiempirical way. Lines and his collaborators used this theory to explain the short-range correlations and their anisotropy in the paramagnetic phase. Later Suzuki et al., Chatterjee and Desai, Mukhopadhyay and Chatterjee applied this theory to the magnetically ordered phase and a tremendous success of the theory has been found in real systems. The success of the CEF theory is discussed in this review. In order to highlight the success of this theory, earlier effective field theories and their improvements over mean field theories e.g., Bethe-Peierls-Weiss method, reaction field approximation, etc., are also discussed in this review for completeness. The beauty of the CEF theory is that it is mean field-like, but captures the essential physics of real systems to a great extent. However, this is a weak correlated theory and as a result is inappropriate for the metallic phase when strong correlations become important. In recent times, transition metal oxides become important due to the discovery of the high-temperature superconductivity and the colossal magnetoresistance phenomena. These oxides seem to be Mott insulators and undergo an insulator to metal transition by applying magnetic field, pressure and by changing

Transition metal oxide as anode interface buffer for impedance spectroscopy

Science.gov (United States)

Xu, Hui; Tang, Chao; Wang, Xu-Liang; Zhai, Wen-Juan; Liu, Rui-Lan; Rong, Zhou; Pang, Zong-Qiang; Jiang, Bing; Fan, Qu-Li; Huang, Wei

2015-12-01

Impedance spectroscopy is a strong method in electric measurement, which also shows powerful function in research of carrier dynamics in organic semiconductors when suitable mathematical physical models are used. Apart from this, another requirement is that the contact interface between the electrode and materials should at least be quasi-ohmic contact. So in this report, three different transitional metal oxides, V2O5, MoO3 and WO3 were used as hole injection buffer for interface of ITO/NPB. Through the impedance spectroscopy and PSO algorithm, the carrier mobilities and I-V characteristics of the NPB in different devices were measured. Then the data curves were compared with the single layer device without the interface layer in order to investigate the influence of transitional metal oxides on the carrier mobility. The careful research showed that when the work function (WF) of the buffer material was just between the work function of anode and the HOMO of the organic material, such interface material could work as a good bridge for carrier injection. Under such condition, the carrier mobility measured through impedance spectroscopy should be close to the intrinsic value. Considering that the HOMO (or LUMO) of most organic semiconductors did not match with the work function of the electrode, this report also provides a method for wide application of impedance spectroscopy to the research of carrier dynamics.

Dendrimer-magnetic nanostructure: a Monte Carlo simulation

Science.gov (United States)

Jabar, A.; Masrour, R.

2017-11-01

In this paper, the magnetic properties of ternary mixed spins (σ,S,q) Ising model on a dendrimer nanostructure are studied using Monte Carlo simulations. The ground state phase diagrams of dendrimer nanostructure with ternary mixed spins σ = 1/2, S = 1 and q = 3/2 Ising model are found. The variation of the thermal total and partial magnetizations with the different exchange interactions, the external magnetic fields and the crystal fields have been also studied. The reduced critical temperatures have been deduced. The magnetic hysteresis cycles have been discussed. In particular, the corresponding magnetic coercive filed values have been deduced. The multiples hysteresis cycles are found. The dendrimer nanostructure has several applications in the medicine.

A new approach for crystallization of copper(ii) oxide hollow nanostructures with superior catalytic and magnetic response

Science.gov (United States)

Singh, Inderjeet; Landfester, Katharina; Chandra, Amreesh; Muñoz-Espí, Rafael

2015-11-01

We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism.We report the synthesis of copper(ii) oxide hollow nanostructures at ambient pressure and close to room temperature by applying the soft templating effect provided by the confinement of droplets in miniemulsion systems. Particle growth can be explained by considering a mechanism that involves both diffusion and reaction control. The catalytic reduction of p-nitrophenol in aqueous media is used as a model reaction to prove the catalytic activity of the materials: the synthesized hollow structures show nearly 100 times higher rate constants than solid CuO microspheres. The kinetic behavior and the order of the reduction reaction change due to the increase of the surface area of the hollow structures. The synthesis also leads to modification of physical properties such as magnetism. Electronic supplementary information (ESI) available: Associated structural and morphological analysis, XPS characterization, BET surface area, catalytic measurements, recycle tests of the catalyst, and magnetic characterizations. See DOI: 10.1039/c5nr05579b

Approach to Multifunctional Device Platform with Epitaxial Graphene on Transition Metal Oxide (Postprint)

Science.gov (United States)

2015-09-23

layers, respectively. 15. SUBJECT TERMS Heterostructures, two-dimensional materials, van der Waals interaction , 2D graphene, metal oxide (TiO2...sample holder with a 10.6 μ m CO2 IR laser . The laser output power was adjusted until the target temperature was reached. The temperature of the sample... Laser Deposited Transition- Metal Carbides for Field-Emission Cathode Coatings. ACS Appl. Mater. Interfaces 5, 9241–9246 (2013). 13. Swift, G. A

Oxidation feature and diffusion mechanism of Zr-based metallic glasses near the glass transition point

Science.gov (United States)

Hu, Zheng; Lei, Xianqi; Wang, Yang; Zhang, Kun

2018-03-01

The oxidation behaviors of as-cast, pre-deformed, and crystallized Zr47.9Ti0.3Ni3.1Cu39.3Al9.4 metallic glasses (MGs) were studied near the glass transition point. The oxidation kinetics of the crystallized MGs followed a parabolic-rate law, and the as-cast and pre-deformed MGs exerted a typical two-stage behavior above the glass transition temperature (T g). Most interesting, pre-deformed treatment can significantly improve the oxidation rate of MGs, as the initial oxidation appeared earlier than for the as-cast MGs, and was accompanied by much thicker oxide scale. The EDS and XPS results showed that the metal Al acted as the preferred scavenger that absorbed intrinsic oxygen in the near-surface region of as-cast MGs. However, a homogeneous mixed layer without Al was observed in the pre-deformed MGs. We speculated the accelerated diffusion of other elements in the MGs was due to the local increase in the free volume and significant shear-induced dilation of the local structure. The results from this study demonstrate that MGs exhibit controllable atomic diffusion during the oxidation process, which can facilitate use in super-cooled liquid region applications.

Giant magnetic anisotropy of rare-earth adatoms and dimers adsorbed by graphene oxide.

Science.gov (United States)

Zhang, Kai-Cheng; Li, Yong-Feng; Liu, Yong; Zhu, Yan; Shi, Li-Bin

2017-05-24

Nowadays, transition-metal adatoms and dimers with giant magnetic anisotropy have attracted much attention due to their potential applications in data storage, spintronics and quantum computations. Using density-functional calculations, we investigated the magnetic anisotropy of the rare-earth adatoms and dimers adsorbed by graphene oxide. Our calculations reveal that the adatoms of Tm, Er and Sm possess giant magnetic anisotropy, typically larger than 40 meV. When the dimers of (Tm,Er,Sm)-Ir are adsorbed onto graphene oxide, the magnetic anisotropy even exceeds 200 meV. The magnetic anisotropy can be tuned by the external electric field as well as the environment.

Emergent magnetism at transition-metal-nanocarbon interfaces.

Science.gov (United States)

Al Ma'Mari, Fatma; Rogers, Matthew; Alghamdi, Shoug; Moorsom, Timothy; Lee, Stephen; Prokscha, Thomas; Luetkens, Hubertus; Valvidares, Manuel; Teobaldi, Gilberto; Flokstra, Machiel; Stewart, Rhea; Gargiani, Pierluigi; Ali, Mannan; Burnell, Gavin; Hickey, B J; Cespedes, Oscar

2017-05-30

Charge transfer at metallo-molecular interfaces may be used to design multifunctional hybrids with an emergent magnetization that may offer an eco-friendly and tunable alternative to conventional magnets and devices. Here, we investigate the origin of the magnetism arising at these interfaces by using different techniques to probe 3d and 5d metal films such as Sc, Mn, Cu, and Pt in contact with fullerenes and rf-sputtered carbon layers. These systems exhibit small anisotropy and coercivity together with a high Curie point. Low-energy muon spin spectroscopy in Cu and Sc-C 60 multilayers show a quick spin depolarization and oscillations attributed to nonuniform local magnetic fields close to the metallo-carbon interface. The hybridization state of the carbon layers plays a crucial role, and we observe an increased magnetization as sp 3 orbitals are annealed into sp 2 -π graphitic states in sputtered carbon/copper multilayers. X-ray magnetic circular dichroism (XMCD) measurements at the carbon K edge of C 60 layers in contact with Sc films show spin polarization in the lowest unoccupied molecular orbital (LUMO) and higher π*-molecular levels, whereas the dichroism in the σ*-resonances is small or nonexistent. These results support the idea of an interaction mediated via charge transfer from the metal and dz -π hybridization. Thin-film carbon-based magnets may allow for the manipulation of spin ordering at metallic surfaces using electrooptical signals, with potential applications in computing, sensors, and other multifunctional magnetic devices.

PREFACE: INERA Workshop: Transition Metal Oxide Thin Films-functional Layers in "Smart windows" and Water Splitting Devices. Parallel session of the 18th International School on Condensed Matter Physics

Science.gov (United States)

2014-11-01

The Special issue presents the papers for the INERA Workshop entitled "Transition Metal Oxides as Functional Layers in Smart windows and Water Splitting Devices", which was held in Varna, St. Konstantin and Elena, Bulgaria, from the 4th-6th September 2014. The Workshop is organized within the context of the INERA "Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures", FP7 Project REGPOT 316309 program, European project of the Institute of Solid State Physics at the Bulgarian Academy of Sciences. There were 42 participants at the workshop, 16 from Sweden, Germany, Romania and Hungary, 11 invited lecturers, and 28 young participants. There were researchers present from prestigious European laboratories which are leaders in the field of transition metal oxide thin film technologies. The event contributed to training young researchers in innovative thin film technologies, as well as thin films characterization techniques. The topics of the Workshop cover the field of technology and investigation of thin oxide films as functional layers in "Smart windows" and "Water splitting" devices. The topics are related to the application of novel technologies for the preparation of transition metal oxide films and the modification of chromogenic properties towards the improvement of electrochromic and termochromic device parameters for possible industrial deployment. The Workshop addressed the following topics: Metal oxide films-functional layers in energy efficient devices; Photocatalysts and chemical sensing; Novel thin film technologies and applications; Methods of thin films characterizations; From the 37 abstracts sent, 21 manuscripts were written and later refereed. We appreciate the comments from all the referees, and we are grateful for their valuable contributions. Guest Editors: Assoc. Prof. Dr.Tatyana Ivanova Prof. DSc Kostadinka Gesheva Prof. DSc Hassan Chamatti Assoc. Prof. Dr. Georgi Popkirov Workshop Organizing Committee Prof

Growth of metal and semiconductor nanostructures using localized photocatalysts

Energy Technology Data Exchange (ETDEWEB)

Shelnutt, John A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Wang, Zhongchun [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Medforth, Craig J. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

2006-03-08

Our overall goal has been to understand and develop a light-driven approach to the controlled growth of novel metal and semiconductor nanostructures and nanomaterials. In this photochemical process, bio-inspired porphyrin-based photocatalysts reduce metal salts in aqueous solutions at ambient temperatures when exposed to visible light, providing metal nucleation and growth centers. The photocatalyst molecules are pre-positioned at the nanoscale to control the location of the deposition of metal and therefore the morphology of the nanostructures that are grown. Self-assembly, chemical confinement, and molecular templating are some of the methods we are using for nanoscale positioning of the photocatalyst molecules. When exposed to light, each photocatalyst molecule repeatedly reduces metal ions from solution, leading to deposition near the photocatalyst and ultimately the synthesis of new metallic nanostructures and nanostructured materials. Studies of the photocatalytic growth process and the resulting nanostructures address a number of fundamental biological, chemical, and environmental issues and draw on the combined nanoscience characterization and multi-scale simulation capabilities of the new DOE Center for Integrated Nanotechnologies at Sandia National Laboratories and the University of Georgia. Our main goals are to elucidate the processes involved in the photocatalytic growth of metal nanomaterials and provide the scientific basis for controlled nanosynthesis. The nanomaterials resulting from these studies have applications in nanoelectronics, photonics, sensors, catalysis, and micromechanical systems. Our specific goals for the past three years have been to understand the role of photocatalysis in the synthesis of dendritic metal (Pt, Pd, Au) nanostructures grown from aqueous surfactant solutions under ambient conditions and the synthesis of photocatalytic porphyrin nanostructures (e.g., nanotubes) as templates for fabrication of photo-active metal

Interplay between magnetic and dielectric phenomena at transition metal oxide interfaces

International Nuclear Information System (INIS)

Schumacher, Daniel

2013-01-01

The present work is concerned with the preparation, characterization and analysis of thin film heterostructures of perovskite oxide materials. Two different systems have been analyzed in detail: La 0.66 Sr 0.33 MnO 3 /SrTiO 3 (LSMO/STO) heterostructures have been investigated in order to understand the unusual occurrence of an exchange bias effect in multilayers of these two oxides. Monocrystalline LSMO single and LSMO/STO bilayers have been grown on STO by both High Oxygen Pressure Sputter Deposition (HSD) and Pulsed Laser Deposition. It was possible to reproduce the Exchange Bias effect in the samples grown by HSD by reducing the oxygen pressure during the layer growth. In fact, the size of the effect can be increased by further reduction of the oxygen pressure. The macroscopic sample analysis by X-ray Diffraction and Vibrating Sample Magnetometry suggests that the occurence of the Exchange Bias effect is linked to oxygen deficiencies in the LSMO layer. By combining X-ray Reflectometry, Polarized Neutron Reflectometry and X-ray Resonant magnetic Scattering (XRMS), the magnetic depth profile of the samples has been determined. By this, a region in LSMO at the interface to STO has been detected, where the magnetic moment is strongly suppressed. By putting together the results of the macroscopic sample analysis and the scattering experiments, an explanation for the occurence of the effect can be given: It is proposed, that a combination of strain and oxygen deficiencies shifts the LSMO at the interface in the antiferromagnetic phase of the LSMO strain vs. doping phase diagram. This interface region thus couples to the ferromagnetic part of the LSMO causing the Exchange Bias effect. The second heterostructure system under investigation in this work are bilayers of La 0.5 Sr 0.5 MnO 3 (LSMO) and BaTiO 3 (BTO). A possible dependence of the interface near magnetic structure of La 1-x Sr x MnO 3 having a doping level x close to the ferromagnetic-antiferromagnetic phase

Interplay between magnetic and dielectric phenomena at transition metal oxide interfaces

Energy Technology Data Exchange (ETDEWEB)

Schumacher, Daniel

2013-10-01

The present work is concerned with the preparation, characterization and analysis of thin film heterostructures of perovskite oxide materials. Two different systems have been analyzed in detail: La{sub 0.66}Sr{sub 0.33}MnO{sub 3}/SrTiO{sub 3} (LSMO/STO) heterostructures have been investigated in order to understand the unusual occurrence of an exchange bias effect in multilayers of these two oxides. Monocrystalline LSMO single and LSMO/STO bilayers have been grown on STO by both High Oxygen Pressure Sputter Deposition (HSD) and Pulsed Laser Deposition. It was possible to reproduce the Exchange Bias effect in the samples grown by HSD by reducing the oxygen pressure during the layer growth. In fact, the size of the effect can be increased by further reduction of the oxygen pressure. The macroscopic sample analysis by X-ray Diffraction and Vibrating Sample Magnetometry suggests that the occurence of the Exchange Bias effect is linked to oxygen deficiencies in the LSMO layer. By combining X-ray Reflectometry, Polarized Neutron Reflectometry and X-ray Resonant magnetic Scattering (XRMS), the magnetic depth profile of the samples has been determined. By this, a region in LSMO at the interface to STO has been detected, where the magnetic moment is strongly suppressed. By putting together the results of the macroscopic sample analysis and the scattering experiments, an explanation for the occurence of the effect can be given: It is proposed, that a combination of strain and oxygen deficiencies shifts the LSMO at the interface in the antiferromagnetic phase of the LSMO strain vs. doping phase diagram. This interface region thus couples to the ferromagnetic part of the LSMO causing the Exchange Bias effect. The second heterostructure system under investigation in this work are bilayers of La{sub 0.5}Sr{sub 0.5}MnO{sub 3} (LSMO) and BaTiO{sub 3} (BTO). A possible dependence of the interface near magnetic structure of La{sub 1-x}Sr{sub x}MnO{sub 3} having a doping level x

Curie temperature and magnetic phase transition of nanostructured ultrathin Fe/GaAs (001). Size dependence and relevance of dipolar coupling

Energy Technology Data Exchange (ETDEWEB)

Meier, Roland

2009-07-01

In the present work the impact of lateral patterning of ultrathin ferromagnetic films down to the nanometer range on the magnetic phase transition has been investigated. In this respect on the one hand a size effect on the Curie temperature and, referring to that, the relevance of dipolar coupling were a matter of particular interest. On the other hand the characteristics of the critical behavior itself, becoming apparent by the accurate evaluation of the curvature shape of the magnetization as a function of temperature at T{sub c}, were analyzed with regard to potential and expected size effects. The investigation of similar nanostructures with respect to an effect on Curie temperature respectively phase transition may draw up a correlation. Therefore more than hundred samples were fabricated for this work extensively by means of MBE (Molecular Beam Epitaxy) and ESL (Electron Beam Epitaxy) methods, measured by MOKE (Magneto-Optical Kerr Effect) technique and systematically evaluated. (orig.)

Investigation of magnetic and magneto-transport properties of ferromagnetic-charge ordered core-shell nanostructures

Science.gov (United States)

Das, Kalipada

2017-10-01

In our present study, we address in detail the magnetic and magneto-transport properties of ferromagnetic-charge ordered core-shell nanostructures. In these core-shell nanostructures, well-known half metallic La0.67Sr0.33MnO3 nanoparticles (average particle size, ˜20 nm) are wrapped by the charge ordered antiferromagnetic Pr0.67Ca0.33MnO3 (PCMO) matrix. The intrinsic properties of PCMO markedly modify it into such a core-shell form. The robustness of the PCMO matrix becomes fragile and melts at an external magnetic field (H) of ˜20 kOe. The analysis of magneto-transport data indicates the systematic reduction of the electron-electron and electron-magnon interactions in the presence of an external magnetic field in these nanostructures. The pronounced training effect appears in this phase separated compound, which was analyzed by considering the second order tunneling through the grain boundaries of the nanostructures. Additionally, the analysis of low field magnetoconductance data supports the second order tunneling and shows the close value of the universal limit (˜1.33).

A general soft-enveloping strategy in the templating synthesis of mesoporous metal nanostructures.

Science.gov (United States)

Fang, Jixiang; Zhang, Lingling; Li, Jiang; Lu, Lu; Ma, Chuansheng; Cheng, Shaodong; Li, Zhiyuan; Xiong, Qihua; You, Hongjun

2018-02-06

Metal species have a relatively high mobility inside mesoporous silica; thus, it is difficult to introduce the metal precursors into silica mesopores and suppress the migration of metal species during a reduction process. Therefore, until now, the controlled growth of metal nanocrystals in a confined space, i.e., mesoporous channels, has been very challenging. Here, by using a soft-enveloping reaction at the interfaces of the solid, liquid, and solution phases, we successfully control the growth of metallic nanocrystals inside a mesoporous silica template. Diverse monodispersed nanostructures with well-defined sizes and shapes, including Ag nanowires, 3D mesoporous Au, AuAg alloys, Pt networks, and Au nanoparticle superlattices are successfully obtained. The 3D mesoporous AuAg networks exhibit enhanced catalytic activities in an electrochemical methanol oxidation reaction. The current soft-enveloping synthetic strategy offers a robust approach to synthesize diverse mesoporous metal nanostructures that can be utilized in catalysis, optics, and biomedicine applications.

Engineering metallic nanostructures for plasmonics and nanophotonics

Science.gov (United States)

Lindquist, Nathan C.; Nagpal, Prashant; McPeak, Kevin M.; Norris, David J.; Oh, Sang-Hyun

2012-03-01

Metallic nanostructures now play an important role in many applications. In particular, for the emerging fields of plasmonics and nanophotonics, the ability to engineer metals on nanometric scales allows the development of new devices and the study of exciting physics. This review focuses on top-down nanofabrication techniques for engineering metallic nanostructures, along with computational and experimental characterization techniques. A variety of current and emerging applications are also covered.

Nanocrystalline transition metal oxides as catalysts in the thermal decomposition of ammonium perchlorate

Energy Technology Data Exchange (ETDEWEB)

Kapoor, Inder Pal Singh; Srivastava, Pratibha; Singh, Gurdip [Department of Chemistry, DDU Gorakhpur University, Gorakhpur (India)

2009-08-15

Nanocrystalline transition metal oxides (NTMOs) have been successfully prepared by three different methods: novel quick precipitation method (Cr{sub 2}O{sub 3} and Fe{sub 2}O{sub 3}); surfactant mediated method (CuO), and reduction of metal complexes with hydrazine as reducing agent (Mn{sub 2}O{sub 3}). The nano particles have been characterized by X-ray diffraction (XRD) which shows an average particle diameter of 35-54 nm. Their catalytic activity was measured in the thermal decomposition of ammonium perchlorate (AP). AP decomposition undergoes a two step process where the addition of metal oxide nanocrystals led to a shifting of the high temperature decomposition peak toward lower temperature. The kinetics of the thermal decomposition of AP and catalyzed AP has also been evaluated using model fitting and isoconversional method. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

A magnetic resonance study of 3d transition metals and thermal donors in silicon

International Nuclear Information System (INIS)

Wezep, D.A. van.

1986-01-01

This thesis describes a study of 3d-transition metal impurities in silicon (titanium and iron in particular) and a study of oxygen-related heat-treatment centers in silicon, both carried out mainly by magnetic resonances techniques like EPR and ENDOR. 119 refs.; 31 figs.; 14 tabs

A metallic metal oxide (Ti5O9)-metal oxide (TiO2) nanocomposite as the heterojunction to enhance visible-light photocatalytic activity.

Science.gov (United States)

Li, L H; Deng, Z X; Xiao, J X; Yang, G W

2015-01-26

Coupling titanium dioxide (TiO2) with other semiconductors is a popular method to extend the optical response range of TiO2 and improve its photon quantum efficiency, as coupled semiconductors can increase the separation rate of photoinduced charge carriers in photocatalysts. Differing from normal semiconductors, metallic oxides have no energy gap separating occupied and unoccupied levels, but they can excite electrons between bands to create a high carrier mobility to facilitate kinetic charge separation. Here, we propose the first metallic metal oxide-metal oxide (Ti5O9-TiO2) nanocomposite as a heterojunction for enhancing the visible-light photocatalytic activity of TiO2 nanoparticles and we demonstrate that this hybridized TiO2-Ti5O9 nanostructure possesses an excellent visible-light photocatalytic performance in the process of photodegrading dyes. The TiO2-Ti5O9 nanocomposites are synthesized in one step using laser ablation in liquid under ambient conditions. The as-synthesized nanocomposites show strong visible-light absorption in the range of 300-800 nm and high visible-light photocatalytic activity in the oxidation of rhodamine B. They also exhibit excellent cycling stability in the photodegrading process. A working mechanism for the metallic metal oxide-metal oxide nanocomposite in the visible-light photocatalytic process is proposed based on first-principle calculations of Ti5O9. This study suggests that metallic metal oxides can be regarded as partners for metal oxide photocatalysts in the construction of heterojunctions to improve photocatalytic activity.

Electronic and magnetic properties of 3d transition metal-doped strontium clusters: Prospective magnetic superatoms

International Nuclear Information System (INIS)

Chauhan, Vikas; Sen, Prasenjit

2013-01-01

Highlights: • Structural, electronic and magnetic properties of TM-Sr clusters are studied using DFT methods. • CrSr 9 and MnSr 10 have enhanced stability in the CrSr n and MnSrn series. • These two clusters behave as magnetic superatoms. • A qualitative understanding of the magnetic coupling between two superatom units is offered. • Reactivity of these superatoms to molecular oxygen also studied. - Abstract: Structural, electronic and magnetic properties of 3d transition metal doped strontium clusters are studied using first-principles electronic structure methods based on density functional theory. Clusters with enhanced kinetic and thermodynamic stability are identified by studying their hardness, second order energy difference and adiabatic spin excitation energy. CrSr 9 and MnSr 10 are found to have enhanced stability. They retain their structural identities in assemblies, and are classified as magnetic superatoms. A qualitative understanding of the magnetic coupling between two cluster units is arrived at. Reactivity of these superatoms with O 2 molecule is also studied. Prospects for using these magnetic superatoms in applications are discussed

Different magnetic properties of rhombohedral and cubic Ni2+ doped indium oxide nanomaterials

Directory of Open Access Journals (Sweden)

Qingbo Sun

2011-12-01

Full Text Available Transition metal ions doped indium oxide nanomaterials were potentially used as a kind of diluted magnetic semiconductors in transparent spintronic devices. In this paper, the influences of Ni2+ doped contents and rhombohedral or cubic crystalline structures of indium oxide on magnetic properties were investigated. We found that the magnetic properties of Ni2+ doped indium oxide could be transferred from room temperature ferromagnetisms to paramagnetic properties with increments of doped contents. Moreover, the different crystalline structures of indium oxide also greatly affected the room temperature ferromagnetisms due to different lattice constants and almost had no effects on their paramagnetic properties. In addition, both the ferromagnetic and paramagnetic properties were demonstrated to be intrinsic and not caused by impurities.

Magnetic properties of 3d-transition metal and rare earth fluoride glasses

International Nuclear Information System (INIS)

Renard, J.P.; Dupas, C.; Velu, E.; Jacobini, C.; Fonteneau, G.; Lucas, J.

1981-01-01

The ac susceptibility of fluoride glasses in the ternary systems PbF 2 -MnF 2 -FeF 3 , ThF 4 -BaF 2 -MnF 2 , ZnF 2 -BaF 2 -RF 3 (R = Dy-Ho) has been studied down to 0.3 K. The susceptibility of rare earth glasses exhibits a broad maximum strongly dependent on the measuring frequency ν while a spin glass transition with a sharp susceptibility cusp nearly independent on ν is observed in 3d-transition metal glasses. Magnetic after effects are observed below the spin freezing temperature. (orig.)

Electronic structure and magnetism in transition metals doped 8-hydroxy-quinoline aluminum.

Science.gov (United States)

Baik, Jeong Min; Shon, Yoon; Lee, Seung Joo; Jeong, Yoon Hee; Kang, Tae Won; Lee, Jong-Lam

2008-10-15

We report the room-temperature ferromagnetism in transition metals (Co, Ni)-doped 8-hydroxy-quinoline aluminum (Alq3) by thermal coevaporation of high purity metal and Alq3 powders. For 5% Co-doped Alq3, a maximum magnetization of approximately 0.33 microB/Co at 10 K was obtained and ferromagnetic behavior was observed up to 300 K. The Co atoms interact chemically with O atoms and provide electrons to Alq3, forming new states acting as electron trap sites. From this, it is suggested that ferromagnetism may be associated with the strong chemical interaction of Co atoms and Alq3 molecules.

Competitive Adsorption of Metals onto Magnetic Graphene Oxide: Comparison with Other Carbonaceous Adsorbents

Directory of Open Access Journals (Sweden)

Jin Hur

2015-01-01

Full Text Available Competitive adsorption isotherms of Cu(II, Pb(II, and Cd(II were examined on a magnetic graphene oxide (GO, multiwalled carbon nanotubes (MWCNTs, and powered activated carbon (PAC. A series of analyses confirmed the successful synthesis of the magnetic GO based on a simple ultrasonification method. Irrespective of the adsorbents, the adsorption was highly dependent on pH, and the adsorption was well described by the Langmuir isotherm model. The maximum adsorption capacities of the adsorbents were generally higher in the order of Pb(II > Cu(II > Cd(II, which is the same as the degree of the electronegativity and the hydrated radius of the metals, suggesting that the metal adsorption may be governed by an ion exchange between positively charged metals and negatively charged surfaces, as well as diffusion of metals into the surface layer. The adsorption of each metal was mostly lower for multi- versus single-metal systems. The antagonistic effects were influenced by solution pH as well as the type of metals, and they were higher in the order of the magnetic GO > MWCNT > PAC. Dissolved HS played a greater role than HS adsorbed onto the adsorbents, competing with the adsorption sites for metal complexation.

Theory of magnetic transition metal nanoclusters on surfaces

Energy Technology Data Exchange (ETDEWEB)

Lounis, S.

2007-04-17

This thesis is motivated by the quest for the understanding and the exploration of complex magnetism provided by atomic scale magnetic clusters deposited on surfaces or embedded in the bulk. Use is made of the density functional theory (DFT). Acting within this framework, we have developed and implemented the treatment of non-collinear magnetism into the Juelich version of the full-potential Korringa-Kohn-Rostoker Green Function (KKR-GF) method. Firstly, the method was applied to 3d transition-metal clusters on different ferromagnetic surfaces. Different types of magnetic clusters where selected. In order to investigate magnetic frustration due to competing interactions within the ad-cluster we considered a (001) oriented surface of fcc metals, a topology which usually does not lead to non-collinear magnetism. We tuned the strength of the magnetic coupling between the ad-clusters and the ferromagnetic surface by varying the substrate from the case of Ni(001) with a rather weak hybridization of the Ni d-states with the adatom d-states to the case of Fe{sub 3ML}/Cu(001) with a much stronger hybridization due to the larger extend of the Fe wavefunctions. On Ni(001), the interaction between the Cr- as well as the Mn-dimer adatoms is of antiferromagnetic nature, which is in competition with the interaction with the substrate atoms. After performing total energy calculations we find that for Cr-dimer the ground state is collinear whereas the Mn-dimer prefers the non-collinear configuration as ground state. Bigger clusters are found to be magnetically collinear. These calculations were extended to 3d multimers on Fe{sub 3ML}/Cu(001). All neighboring Cr(Mn) moments in the compact tetramer are antiferromagnetically aligned in-plane, with the directions slightly tilted towards (outwards from) the substrate to gain some exchange interaction energy. The second type of frustration was investigated employing a Ni(111) surface, a surface with a triangular lattice of atoms, were

Reduced graphene oxide wrapped Ag nanostructures for enhanced SERS activity

Science.gov (United States)

Nair, Anju K.; Kala, M. S.; Thomas, Sabu; Kalarikkal, Nandakumar

2018-04-01

Graphene - metal nanoparticle hybrids have received great attention due to their unique electronic properties, large specific surface area, very high conductivity and more charge transfer. Thus, it is extremely advantages to develop a simple and efficient process to disperse metal nanostructures over the surface of graphene sheets. Herein, we report a hydrothermal assisted strategy for developing reduced graphene oxide /Ag nanomorphotypes (cube, wire) for surface enhanced Raman scattering (SERS) applications, considering the advantages of synergistic effect of graphene and plasmonic properties of Ag nanomorphotypes.

Nanostructured metal foams: synthesis and applications

Energy Technology Data Exchange (ETDEWEB)

Luther, Erik P [Los Alamos National Laboratory; Tappan, Bryce [Los Alamos National Laboratory; Mueller, Alex [Los Alamos National Laboratory; Mihaila, Bogdan [Los Alamos National Laboratory; Volz, Heather [Los Alamos National Laboratory; Cardenas, Andreas [Los Alamos National Laboratory; Papin, Pallas [Los Alamos National Laboratory; Veauthier, Jackie [Los Alamos National Laboratory; Stan, Marius [Los Alamos National Laboratory

2009-01-01

Fabrication of monolithic metallic nanoporous materials is difficult using conventional methodology. Here they report a relatively simple method of synthesizing monolithic, ultralow density, nanostructured metal foams utilizing self-propagating combustion synthesis of novel metal complexes containing high nitrogen energetic ligands. Nanostructured metal foams are formed in a post flame-front dynamic assembly with densities as low as 0.011 g/cc and surface areas as high as 270 m{sup 2}/g. They have produced metal foams via this method of titanium, iron, cobalt, nickel, zirconium, copper, palladium, silver, hafnium, platinum and gold. Microstructural features vary as a function of composition and process parameters. Applications for the metal foams are discussed including hydrogen absorption in palladium foams. A model for the sorption kinetics of hydrogen in the foams is presented.

Metal complex-based templates and nanostructures for magnetic resonance/optical multimodal imaging agents

NARCIS (Netherlands)

Galindo Millan, Jealemy

2012-01-01

In this thesis, new approaches directed towards simple and functional imaging agents (IAs) for magnetic resonance (MR) and fluorescence multimodal imaging are proposed. In Chapter 3, hybrid silver nanostructures (hAgNSs), grown using a polyamino carboxylic acid scaffold, namely

Understanding the biological responses of nanostructured metals and surfaces

Science.gov (United States)

Lowe, Terry C.; Reiss, Rebecca A.

2014-08-01

Metals produced by Severe Plastic Deformation (SPD) offer distinct advantages for medical applications such as orthopedic devices, in part because of their nanostructured surfaces. We examine the current theoretical foundations and state of knowledge for nanostructured biomaterials surface optimization within the contexts that apply to bulk nanostructured metals, differentiating how their microstructures impact osteogenesis, in particular, for Ultrafine Grained (UFG) titanium. Then we identify key gaps in the research to date, pointing out areas which merit additional focus within the scientific community. For example, we highlight the potential of next-generation DNA sequencing techniques (NGS) to reveal gene and non-coding RNA (ncRNA) expression changes induced by nanostructured metals. While our understanding of bio-nano interactions is in its infancy, nanostructured metals are already being marketed or developed for medical devices such as dental implants, spinal devices, and coronary stents. Our ability to characterize and optimize the biological response of cells to SPD metals will have synergistic effects on advances in materials, biological, and medical science.

Understanding the biological responses of nanostructured metals and surfaces

International Nuclear Information System (INIS)

Lowe, Terry C; A Reiss, Rebecca

2014-01-01

Metals produced by Severe Plastic Deformation (SPD) offer distinct advantages for medical applications such as orthopedic devices, in part because of their nanostructured surfaces. We examine the current theoretical foundations and state of knowledge for nanostructured biomaterials surface optimization within the contexts that apply to bulk nanostructured metals, differentiating how their microstructures impact osteogenesis, in particular, for Ultrafine Grained (UFG) titanium. Then we identify key gaps in the research to date, pointing out areas which merit additional focus within the scientific community. For example, we highlight the potential of next-generation DNA sequencing techniques (NGS) to reveal gene and non-coding RNA (ncRNA) expression changes induced by nanostructured metals. While our understanding of bio-nano interactions is in its infancy, nanostructured metals are already being marketed or developed for medical devices such as dental implants, spinal devices, and coronary stents. Our ability to characterize and optimize the biological response of cells to SPD metals will have synergistic effects on advances in materials, biological, and medical science

Enhanced electrochemical water oxidation: the impact of nanoclusters and nanocavities

NARCIS (Netherlands)

Zhang, X.; Cao, C.; Bieberle, A.

2017-01-01

The structures of transition metal surfaces and metal oxides are commonly believed to have a significant effect on the catalytic reactions. Density functional theory calculations are therefore used in this study to investigate the oxygen evolution reaction (OER) over nanostructured, i.e. nanocluster

Effect of surfactant for magnetic properties of iron oxide nanoparticles

Energy Technology Data Exchange (ETDEWEB)

Haracz, S. [Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań (Poland); Hilgendorff, M. [Freie Universität Berlin, Fachbereich Physik, Arnimalle 14, 14195 Berlin (Germany); Rybka, J.D. [Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań (Poland); Giersig, M. [Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89B, 61-614 Poznań (Poland); Freie Universität Berlin, Fachbereich Physik, Arnimalle 14, 14195 Berlin (Germany)

2015-12-01

Highlights: • Dynamic behavior of magnetic nanoparticles. • Synthesis of iron oxide nanoparticles. • Effect of surfactant for magnetic properties. - Abstract: For different medical applications nanoparticles (NPs) with well-defined magnetic properties have to be used. Coating ligand can change the magnetic moment on the surface of nanostructures and therefore the magnetic behavior of the system. Here we investigated magnetic NPs in a size of 13 nm conjugated with four different kinds of surfactants. The surface anisotropy and the magnetic moment of the system were changed due to the presence of the surfactant on the surface of iron oxide NPs.

Wettability transition induced transformation and entrapment of polymer nanostructures in cylindrical nanopores.

Science.gov (United States)

Feng, Xunda; Mei, Shilin; Jin, Zhaoxia

2011-12-06

We apply the concept of wettability transition to manipulate the morphology and entrapment of polymer nanostructures inside cylindrical nanopores of anodic aluminum oxide (AAO) membranes. When AAO/polystyrene (PS) hybrids, i.e., AAO/PS nanorods or AAO/PS nanotubes, are immersed into a polyethylene glycol (PEG) reservoir above the glass transition temperature of PS, a wettability transition from wetting to nonwetting of PS can be triggered due to the invasion of the more wettable PEG melt. The wettability transition enables us to develop a nondestructive method to entrap hemispherically capped nanorods inside nanopores. Moreover, we can obtain single nanorods with the desired aspect ratio by further dissolving the AAO template, in contrast to the drawbacks of nonuniformity or destructiveness from the conventional ultrasonication method. In the case of AAO/PS nanotubes, the wettability transition induced dewetting of PS nanotube walls results in the disconnection and entrapment of nonwetting PS domains (i.e., nanospheres, nanocapsules, or capped nanorods). Moreover, PEG is then washed to recover the pristine wettability of PS on the alumina surface; further annealing of the PS nanospheres inside AAO nanopores under vacuum can generate some unique nanostructures, particularly semicylindrical nanorods. © 2011 American Chemical Society

Toxicity of Transition Metal Oxide Nanoparticles: Recent Insights from in vitro Studies

Directory of Open Access Journals (Sweden)

Robert S. Aronstam

2010-10-01

Full Text Available Nanotechnology has evolved to play a prominent role in our economy. Increased use of nanomaterials poses potential human health risk. It is therefore critical to understand the nature and origin of the toxicity imposed by nanomaterials (nanotoxicity. In this article we review the toxicity of the transition metal oxides in the 4th period that are widely used in industry and biotechnology. Nanoparticle toxicity is compellingly related to oxidative stress and alteration of calcium homeostasis, gene expression, pro-inflammatory responses, and cellular signaling events. The precise physicochemical properties that dictate the toxicity of nanoparticles have yet to be defined, but may include element-specific surface catalytic activity (e.g., metallic, semiconducting properties, nanoparticle uptake, or nanoparticle dissolution. These in vitro studies substantially advance our understanding in mechanisms of toxicity, which may lead to safer design of nanomaterials.

Magnetic coupling at rare earth ferromagnet/transition metal ferromagnet interfaces: A comprehensive study of Gd/Ni

Science.gov (United States)

Higgs, T. D. C.; Bonetti, S.; Ohldag, H.; Banerjee, N.; Wang, X. L.; Rosenberg, A. J.; Cai, Z.; Zhao, J. H.; Moler, K. A.; Robinson, J. W. A.

2016-07-01

Thin film magnetic heterostructures with competing interfacial coupling and Zeeman energy provide a fertile ground to study phase transition between different equilibrium states as a function of external magnetic field and temperature. A rare-earth (RE)/transition metal (TM) ferromagnetic multilayer is a classic example where the magnetic state is determined by a competition between the Zeeman energy and antiferromagnetic interfacial exchange coupling energy. Technologically, such structures offer the possibility to engineer the macroscopic magnetic response by tuning the microscopic interactions between the layers. We have performed an exhaustive study of nickel/gadolinium as a model system for understanding RE/TM multilayers using the element-specific measurement technique x-ray magnetic circular dichroism, and determined the full magnetic state diagrams as a function of temperature and magnetic layer thickness. We compare our results to a modified Stoner-Wohlfarth-based model and provide evidence of a thickness-dependent transition to a magnetic fan state which is critical in understanding magnetoresistance effects in RE/TM systems. The results provide important insight for spintronics and superconducting spintronics where engineering tunable magnetic inhomogeneity is key for certain applications.

Atomic-Resolution Visualization of Distinctive Chemical Mixing Behavior of Ni, Co and Mn with Li in Layered Lithium Transition-Metal Oxide Cathode Materials

Energy Technology Data Exchange (ETDEWEB)

Yan, Pengfei; Zheng, Jianming; Lv, Dongping; Wei, Yi; Zheng, Jiaxin; Wang, Zhiguo; Kuppan, Saravanan; Yu, Jianguo; Luo, Langli; Edwards, Danny J.; Olszta, Matthew J.; Amine, Khalil; Liu, Jun; Xiao, Jie; Pan, Feng; Chen, Guoying; Zhang, Jiguang; Wang, Chong M.

2015-07-06

Capacity and voltage fading of layer structured cathode based on lithium transition metal oxide is closely related to the lattice position and migration behavior of the transition metal ions. However, it is scarcely clear about the behavior of each of these transition metal ions. We report direct atomic resolution visualization of interatomic layer mixing of transition metal (Ni, Co, Mn) and lithium ions in layer structured oxide cathodes for lithium ion batteries. Using chemical imaging with aberration corrected scanning transmission electron microscope (STEM) and DFT calculations, we discovered that in the layered cathodes, Mn and Co tend to reside almost exclusively at the lattice site of transition metal (TM) layer in the structure or little interlayer mixing with Li. In contrast, Ni shows high degree of interlayer mixing with Li. The fraction of Ni ions reside in the Li layer followed a near linear dependence on total Ni concentration before reaching saturation. The observed distinctively different behavior of Ni with respect to Co and Mn provides new insights on both capacity and voltage fade in this class of cathode materials based on lithium and TM oxides, therefore providing scientific basis for selective tailoring of oxide cathode materials for enhanced performance.

Transition metal-modified zinc oxides for UV and visible light photocatalysis.

Science.gov (United States)

Bloh, J Z; Dillert, R; Bahnemann, D W

2012-11-01

In order to use photocatalysis with solar light, finding more active and especially visible light active photocatalysts is a very important challenge. Also, studies of these photocatalysts should employ a standardized test procedure so that their results can be accurately compared and evaluated with one another. A systematic study of transition metal-modified zinc oxide was conducted to determine whether they are suitable as visible light photocatalysts. The photocatalytic activity of ZnO modified with eight different transition metals (Cu, Co, Fe, Mn, Ni, Ru, Ti, Zr) in three different concentrations (0.01, 0.1, and 1 at.%) was investigated under irradiation with UV as well as with visible light. The employed activity test is the gas-phase degradation of acetaldehyde as described by the ISO standard 22197-2. The results suggest that the UV activity can be improved with almost any modification element and that there exists an optimal modification ratio at about 0.1 at.%. Additionally, Mn- and Ru-modified ZnO display visible light activity. Especially the Ru-modified ZnO is highly active and surpasses the visible light activity of all studied titania standards. These findings suggest that modified zinc oxides may be a viable alternative to titanium dioxide-based catalysts for visible light photocatalysis. Eventually, possible underlying mechanisms are proposed and discussed.

Geometry and magnetism of L10 nanostructures

International Nuclear Information System (INIS)

Sorge, K.D.; Skomski, R.; Daniil, M.; Michalski, S.; Gao, L.; Zhou, J.; Yan, M.; Sui, Y.; Kirby, R.D.; Liou, S.H.; Sellmyer, D.J.

2005-01-01

The fabrication and magnetism of L1 0 nanostructures with different shapes (such as nanoparticles and nanotubes) is investigated. These nanostructures are produced by hydrogen processing and focused ion beam milling. The structures exhibit interesting reversal modes and are of present or potential interest for sensors and imaging, as well as magnetic recording

Aerobic Transition-Metal-Free Synthesis of 2,3-Diarylindoles and 5-Aryluracils via Oxidative Nucleophilic Substitution of Hydrogen Pathway

Energy Technology Data Exchange (ETDEWEB)

Yu, Jin; Moon, Hye Ran; Kim, Su Yeon; Kim, Jae Nyoung [Chonnam National Un iversity, Gwangju (Korea, Republic of)

2016-01-15

2,3-diarylindoles and 5-aryluracils were synthesized by ONSH pathway under transition-metal-free conditions in good to moderate yields using molecular oxygen as an oxidant. As 2,3-diarylindoles have been found in many biologically important compounds, the synthesis of this scaffold has received much attention. Most frequently, 2,3-diarylindoles have been prepared via palladium-catalyzed arylations of 2-arylindole with bromoarenes. During our recent transition metal-catalyzed arylations of indoles and uracils, we were interested in the arylation in the absence of an expensive transition metal catalyst.

Metal Nanoparticles and Carbon-Based Nanostructures as Advanced Materials for Cathode Application in Dye-Sensitized Solar Cells

Directory of Open Access Journals (Sweden)

Pietro Calandra

2010-01-01

Full Text Available We review the most advanced methods for the fabrication of cathodes for dye-sensitized solar cells employing nanostructured materials. The attention is focused on metal nanoparticles and nanostructured carbon, among which nanotubes and graphene, whose good catalytic properties make them ideal for the development of counter electrode substrates, transparent conducting oxide, and advanced catalyst materials.

Elucidation of the electrochromic mechanism of nanostructured iron oxides films

Energy Technology Data Exchange (ETDEWEB)

Garcia-Lobato, M.A.; Martinez, Arturo I.; Castro-Roman, M. [Center for Research and Advanced Studies of the National Polytechnic Institute, Cinvestav Campus Saltillo, Carr. Saltillo-Monterrey Km. 13, Ramos Arizpe, Coah. 25900 (Mexico); Perry, Dale L. [Mail Stop 70A1150, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 (United States); Zarate, R.A. [Departamento de Fisica, Facultad de Ciencias, Universidad Catolica del Norte, Casilla 1280, Antofagasta (Chile); Escobar-Alarcon, L. (Departamento de Fisica, Instituto Nacional de Investigaciones Nucleares, A.P. 18-1027, 11801 Mexico)

2011-02-15

Nanostructured hematite thin films were electrochemically cycled in an aqueous solution of LiOH. Through optical, structural, morphological, and magnetic measurements, the coloration mechanism of electrochromic iron oxide thin films was elucidated. The conditions for double or single electrochromic behavior are given in this work. During the electrochemical cycling, it was found that topotactic transformations of hexagonal crystal structures are favored; i.e. {alpha}-Fe{sub 2}O{sub 3} to Fe(OH){sub 2} and subsequently to {delta}-FeOOH. These topotactic redox reactions are responsible for color changes of iron oxide films. (author)

Spin-exchange interaction between transition metals and metalloids in soft-ferromagnetic metallic glasses

Science.gov (United States)

Das, Santanu; Choudhary, Kamal; Chernatynskiy, Aleksandr; Choi Yim, Haein; Bandyopadhyay, Asis K.; Mukherjee, Sundeep

2016-06-01

High-performance magnetic materials have immense industrial and scientific importance in wide-ranging electronic, electromechanical, and medical device technologies. Metallic glasses with a fully amorphous structure are particularly suited for advanced soft-magnetic applications. However, fundamental scientific understanding is lacking for the spin-exchange interaction between metal and metalloid atoms, which typically constitute a metallic glass. Using an integrated experimental and molecular dynamics approach, we demonstrate the mechanism of electron interaction between transition metals and metalloids. Spin-exchange interactions were investigated for a Fe-Co metallic glass system of composition [(Co1-x Fe x )0.75B0.2Si0.05]96Cr4. The saturation magnetization increased with higher Fe concentration, but the trend significantly deviated from simple rule of mixtures. Ab initio molecular dynamics simulation was used to identify the ferromagnetic/anti-ferromagnetic interaction between the transition metals and metalloids. The overlapping band-structure and density of states represent ‘Stoner type’ magnetization for the amorphous alloys in contrast to ‘Heisenberg type’ in crystalline iron. The enhancement of magnetization by increasing iron was attributed to the interaction between Fe 3d and B 2p bands, which was further validated by valence-band study.

Thermal radiative near field transport between vanadium dioxide and silicon oxide across the metal insulator transition

Energy Technology Data Exchange (ETDEWEB)

Menges, F.; Spieser, M.; Riel, H.; Gotsmann, B., E-mail: bgo@zurich.ibm.com [IBM Research-Zurich, Säumerstrasse 4, CH-8803 Rüschlikon (Switzerland); Dittberner, M. [IBM Research-Zurich, Säumerstrasse 4, CH-8803 Rüschlikon (Switzerland); Photonics Laboratory, ETH Zurich, 8093 Zurich (Switzerland); Novotny, L. [Photonics Laboratory, ETH Zurich, 8093 Zurich (Switzerland); Passarello, D.; Parkin, S. S. P. [IBM Almaden Research Center, 650 Harry Road, San Jose, California 95120 (United States)

2016-04-25

The thermal radiative near field transport between vanadium dioxide and silicon oxide at submicron distances is expected to exhibit a strong dependence on the state of vanadium dioxide which undergoes a metal-insulator transition near room temperature. We report the measurement of near field thermal transport between a heated silicon oxide micro-sphere and a vanadium dioxide thin film on a titanium oxide (rutile) substrate. The temperatures of the 15 nm vanadium dioxide thin film varied to be below and above the metal-insulator-transition, and the sphere temperatures were varied in a range between 100 and 200 °C. The measurements were performed using a vacuum-based scanning thermal microscope with a cantilevered resistive thermal sensor. We observe a thermal conductivity per unit area between the sphere and the film with a distance dependence following a power law trend and a conductance contrast larger than 2 for the two different phase states of the film.

Electronic and magnetic properties of SnS2 monolayer doped with 4d transition metals

Science.gov (United States)

Xiao, Wen-Zhi; Xiao, Gang; Rong, Qing-Yan; Chen, Qiao; Wang, Ling-Ling

2017-09-01

We investigate the electronic structures and magnetic properties of SnS2 monolayers substitutionally doped with 4-d transition-metal through systematic first principles calculations. The doped complexes exhibit interesting electronic and magnetic behaviors, depending on the interplay between crystal field splitting, Hund's rule, and 4d levels. The system doped with Y is nonmagnetic metal. Both the Zr- and Pd-doped systems remain nonmagnetic semiconductors. Doping results in half-metallic states for Nb-, Ru-, Rh-, Ag, and Cd doped cases, and magnetic semiconductors for systems with Mo and Tc dopants. In particular, the Nb- and Mo-doped systems display long-ranged ferromagnetic ordering with Curie temperature above room temperature, which are primarily attributable to the double-exchange mechanism, and the p-d/p-p hybridizations, respectively. Moreover, The Mo-doped system has excellent energetic stability and flexible mechanical stability, and also possesses remarkable dynamic and thermal (500 K) stability. Our studies demonstrate that Nb- and Mo-doped SnS2 monolayers are promising candidates for preparing 2D diluted magnetic semiconductors, and hence will be a helpful clue for experimentalists.

Number of outer electrons as descriptor for adsorption processes on transition metals and their oxides

DEFF Research Database (Denmark)

Calle-Vallejo, Federico; Inoglu, Nilay G.; Su, Hai-Yan

2013-01-01

The trends in adsorption energies of the intermediates of the oxygen reduction and evolution reactions on transition metals and their oxides are smoothly captured by the number of outer electrons. This unique descriptor permits the construction of predictive adsorption-energy grids and explains t...

Comparative evaluation of different nanostructured metal oxides for preparation of clinically useful 99Mo/99mTc generators

International Nuclear Information System (INIS)

Ram, Ramu; Chakravarty, Rubel; Dash, Ashutosh

2015-01-01

The potential of nanostructured metal oxides such as nanotitania, nanozirconia, nanoalumina and mesoporous alumina, as new generation sorbent materials for preparation of 99 Mo/ 99m Tc generator has recently been demonstrated. A comparative assessment of such materials is essential for determination of their suitability for preparation of clinically useful generators using (n,γ) 99 Mo. Characteristics which were compared included the sorption capacity, shelf-life of the generator, radioactive concentration and purity of 99m Tc for radiopharmaceutical applications. Mesoporous alumina was identified as the most suitable sorbent for ensuring sustainable production of clinical grade 99 Mo/ 99m Tc generators using low specific activity 99 Mo. (author)

Noncollinear magnetism in manganese nanostructures

Czech Academy of Sciences Publication Activity Database

Zelený, Martin; Šob, Mojmír; Hafner, J.

2009-01-01

Roč. 80, č. 14 (2009), 144414/1-144414/19 ISSN 1098-0121 R&D Projects: GA AV ČR IAA100100920; GA MŠk OC09011 Institutional research plan: CEZ:AV0Z20410507 Keywords : magnetism of nanostructures * nanowires * noncollinear magnetism * manganese Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.475, year: 2009

Nanostructured Gas Sensors for Health Care: An Overview

Science.gov (United States)

Kaushik, Ajeet; Kumar, Rajesh; Jayant, Rahul Dev; Nair, Madhavan

2015-01-01

Nanostructured platforms have been utilized for fabrication of small, sensitive and reliable gas sensing devices owing to high functionality, enhanced charge transport and electro-catalytic property. As a result of globalization, rapid, sensitive and selective detection of gases in environment is essential for health care and security. Nonmaterial such as metal, metal oxides, organic polymers, and organic-inorganic hybrid nanocomposites exhibit interesting optical, electrical, magnetic and molecular properties, and hence are found potential gas sensing materials. Morphological, electrical, and optical properties of such nanostructures can be tailored via controlling the precursor concentration and synthesis conditions resulting to achieve desired sensing. This review presents applications of nano-enabling gas sensors to detect gases for environment monitoring. The recent update, challenges, and future vision for commercial applications of such sensor are also described here. PMID:26491544

Engineering Metal Nanostructure for SERS Application

Directory of Open Access Journals (Sweden)

Yanqin Cao

2013-01-01

Full Text Available Surface-enhanced Raman scattering (SERS has attracted great attention due to its remarkable enhancement and excellent selectivity in the detection of various molecules. Noble metal nanomaterials have usually been employed for producing substrates that can be used in SERS because of their unique local plasma resonance. As the SERS enhancement of signals depends on parameters such as size, shape, morphology, arrangement, and dielectric environment of the nanostructure, there have been a number of studies on tunable nanofabrication and synthesis of noble metals. In this work, we will illustrate progress in engineering metallic nanostructures with various morphologies using versatile methods. We also discuss their SERS applications in different fields and the challenges.

Nanostructured core-shell electrode materials for electrochemical capacitors

Science.gov (United States)

Jiang, Long-bo; Yuan, Xing-zhong; Liang, Jie; Zhang, Jin; Wang, Hou; Zeng, Guang-ming

2016-11-01

Core-shell nanostructure represents a unique system for applications in electrochemical energy storage devices. Owing to the unique characteristics featuring high power delivery and long-term cycling stability, electrochemical capacitors (ECs) have emerged as one of the most attractive electrochemical storage systems since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review aims to summarize recent progress on core-shell nanostructures for advanced supercapacitor applications in view of their hierarchical architecture which not only create the desired hierarchical porous channels, but also possess higher electrical conductivity and better structural mechanical stability. The core-shell nanostructures include carbon/carbon, carbon/metal oxide, carbon/conducting polymer, metal oxide/metal oxide, metal oxide/conducting polymer, conducting polymer/conducting polymer, and even more complex ternary core-shell nanoparticles. The preparation strategies, electrochemical performances, and structural stabilities of core-shell materials for ECs are summarized. The relationship between core-shell nanostructure and electrochemical performance is discussed in detail. In addition, the challenges and new trends in core-shell nanomaterials development have also been proposed.

Transition metal atoms absorbed on MoS2/h-BN heterostructure: stable geometries, band structures and magnetic properties.

Science.gov (United States)

Wu, Yanbing; Huang, Zongyu; Liu, Huating; He, Chaoyu; Xue, Lin; Qi, Xiang; Zhong, Jianxin

2018-06-15

We have studied the stable geometries, band structures and magnetic properties of transition-metal (V, Cr, Mn, Fe, Co and Ni) atoms absorbed on MoS2/h-BN heterostructure systems by first-principles calculations. By comparing the adsorption energies, we find that the adsorbed transition metal (TM) atoms prefer to stay on the top of Mo atoms. The results of the band structure without spin-orbit coupling (SOC) interaction indicate that the Cr-absorbed systems behave in a similar manner to metals, and the Co-absorbed system exhibits a half-metallic state. We also deduce that the V-, Mn-, Fe-absorbed systems are semiconductors with 100% spin polarization at the HOMO level. The Ni-absorbed system is a nonmagnetic semiconductor. In contrast, the Co-absorbed system exhibits metallic state, and the bandgap of V-absorbed system decreases slightly according to the SOC calculations. In addition, the magnetic moments of all the six TM atoms absorbed on the MoS2/h-BN heterostructure systems decrease when compared with those of their free-standing states.

Point-contact spectroscopy of unsaturates oxides of transition metals and the problem of zero anomalies

International Nuclear Information System (INIS)

Tulina, N.A.

1985-01-01

A study was made of point-contact spectra of oxides WO 2 , ReO 3 , MoO 2 with metallic conductivity. It is shown that zero anomalies often observed in transition metal spectra are due to a higher-type oxide interlayer in the vicinity of a point contact. There are no zero anomalies in the point-contact spectra of heterocontacts Zn-MoO 2 (broken crystal) obtained directly in a helium cryostal. When studying such heterocontacts, major maxima of electron- phonon interaction in MoO 2 were determined on the energy scale hω sub(TA) approximately 28 MeV, hω sub(LA) approximately 41 MeV

Precipitation synthesis and magnetic properties of self-assembled magnetite-chitosan nanostructures

Energy Technology Data Exchange (ETDEWEB)

Bezdorozhev, Oleksii; Kolodiazhnyi, Taras; Vasylkiv, Oleg, E-mail: oleg.vasylkiv@nims.go.jp

2017-04-15

This paper reports the synthesis and magnetic properties of unique magnetite-chitosan nanostructures synthesized by the chemical precipitation of magnetite nanoparticles in the presence of chitosan. The influence of varying synthesis parameters on the morphology of the magnetic composites is determined. Depending on the synthesis parameters, magnetite-chitosan nanostructures of spherical (9–18 nm), rice-seed-like (75–290 nm) and lumpy (75–150 nm) shapes were obtained via self-assembly. Spherical nanostructures encapsulated by a 9–15 nm chitosan layer were assembled as well. The prospective morphology of the nanostructures is combined with their excellent magnetic characteristics. It was found that magnetite-chitosan nanostructures are ferromagnetic and pseudo-single domain. Rice-seed-like nanostructures exhibited a coercivity of 140 Oe and saturation magnetization of 56.7 emu/g at 300 K. However, a drop in the magnetic properties was observed for chitosan-coated spherical nanostructures due to the higher volume fraction of chitosan. - Highlights: • Magnetite-chitosan nanostructures are synthesized via self-assembly. • Different morphology can be obtained by adjusting the synthesis parameters. • An attractive combination of magnetic properties and morphology is obtained. • Magnetite-chitosan nanostructures are ferrimagnetic and pseudo-single domain.

Precipitation synthesis and magnetic properties of self-assembled magnetite-chitosan nanostructures

International Nuclear Information System (INIS)

Bezdorozhev, Oleksii; Kolodiazhnyi, Taras; Vasylkiv, Oleg

2017-01-01

This paper reports the synthesis and magnetic properties of unique magnetite-chitosan nanostructures synthesized by the chemical precipitation of magnetite nanoparticles in the presence of chitosan. The influence of varying synthesis parameters on the morphology of the magnetic composites is determined. Depending on the synthesis parameters, magnetite-chitosan nanostructures of spherical (9–18 nm), rice-seed-like (75–290 nm) and lumpy (75–150 nm) shapes were obtained via self-assembly. Spherical nanostructures encapsulated by a 9–15 nm chitosan layer were assembled as well. The prospective morphology of the nanostructures is combined with their excellent magnetic characteristics. It was found that magnetite-chitosan nanostructures are ferromagnetic and pseudo-single domain. Rice-seed-like nanostructures exhibited a coercivity of 140 Oe and saturation magnetization of 56.7 emu/g at 300 K. However, a drop in the magnetic properties was observed for chitosan-coated spherical nanostructures due to the higher volume fraction of chitosan. - Highlights: • Magnetite-chitosan nanostructures are synthesized via self-assembly. • Different morphology can be obtained by adjusting the synthesis parameters. • An attractive combination of magnetic properties and morphology is obtained. • Magnetite-chitosan nanostructures are ferrimagnetic and pseudo-single domain.

Mechanochemical synthesis of graphene oxide-supported transition metal catalysts for the oxidation of isoeugenol to vanillin.

Science.gov (United States)

Franco, Ana; De, Sudipta; Balu, Alina M; Garcia, Araceli; Luque, Rafael

2017-01-01

Vanillin is one of the most commonly used natural products, which can also be produced from lignin-derived feedstocks. The chemical synthesis of vanillin is well-established in large-scale production from petrochemical-based starting materials. To overcome this problem, lignin-derived monomers (such as eugenol, isoeugenol, ferulic acid etc.) have been effectively used in the past few years. However, selective and efficient production of vanillin from these feedstocks still remains an issue to replace the existing process. In this work, new transition metal-based catalysts were proposed to investigate their efficiency in vanillin production. Reduced graphene oxide supported Fe and Co catalysts showed high conversion of isoeugenol under mild reaction conditions using H 2 O 2 as oxidizing agent. Fe catalysts were more selective as compared to Co catalysts, providing a 63% vanillin selectivity at 61% conversion in 2 h. The mechanochemical process was demonstrated as an effective approach to prepare supported metal catalysts that exhibited high activity for the production of vanillin from isoeugenol.

Controlling the flux dynamics in superconductors by nanostructured magnetic arrays

Science.gov (United States)

Kapra, Andrey

In this thesis we investigate theoretically how the critical current jc of nano-engineered mesoscopic superconducting film can be improved and how one can control the dynamics of the magnetic flux, e.g., the transition from flux-pinned to flux-flow regime, using arrays of magnetic nanostructures. In particularly we investigate: (1) Vortex transport phenomena in superconductors with deposited ferromagnetic structures on top, and the influence of the sample geometry on the critical parameters and on the vortex configurations. Changing geometry of the magnetic bars and magnetization of the bars will affect the critical current jc of the superconducting film. Such nanostructured ferromagnets strongly alter the vortex structure in its neighborhood. The influence of geometry, position and magnetization of the ferromagnet (single bar or regular lattice of the bars) on the critical parameters of the superconductor is investigated. (2) Effect of flux confinement in narrow superconducting channels with zigzag-shaped banks: the flux motion is confined in the transverse (perpendicular) direction of a diamond-cell-shape channel. The matching effect for the magnetic flux is found in the system relevantless of boundary condition. We discuss the dynamics of vortices in the samples and vortex pattern formation in the channel. We show how the inclusion of higher-Tc superconductor into the sample can lead to enhanced properties of the system. By adding an external driving force, we study the vortex dynamics. The different dynamic regimes are discussed. They allowed an effective control of magnetic flux in superconductors.

Photoinduced Coherent Spin Fluctuation in Primary Dynamics of Insulator to Metal Transition in Perovskite Cobalt Oxide

Directory of Open Access Journals (Sweden)

Arima T.

2013-03-01

Full Text Available Coherent spin fluctuation was detected in the photoinduced Mott insulator-metal transition in perovskite cobalt oxide by using 3 optical-cycle infrared pulse. Such coherent spin fluctuation is driven by the perovskite distortion changing orbital gap.

Sensitivity, selectivity and stability of tin oxide nanostructures on large area arrays of microhotplates

Science.gov (United States)

Panchapakesan, Balaji; Cavicchi, Richard; Semancik, Steve; DeVoe, Don L.

2006-01-01

In this paper, the sensitivity, stability and selectivity of nanoparticle engineered tin oxide (SnO2) are reported, for microhotplate chemical sensing applications. 16 Å of metals such as nickel, cobalt, iron, copper and silver were selectively evaporated onto each column of the microhotplate array. Following evaporation, the microhotplates were heated to 500 °C and SnO2 was deposited on top of the microhotplates using a self-aligned chemical vapour deposition process. Scanning electron microscopy characterization revealed control of SnO2 nanostructures in the range of 20-121 nm. Gas sensing in seven different hydrocarbons revealed that metal nanoparticles that helped in producing faster nucleation of SnO2 resulted in smaller grain size and higher sensitivity. Sensitivity as a function of concentration and grain size is addressed for tin oxide nanostructures. Smaller grain sizes resulted in higher sensitivity of tin oxide nanostructures. Temperature programmed sensing of the devices yielded shape differences in the response between air and methanol, illustrating selectivity. Spiderweb plots were used to monitor the materials programmed selectivity. The shape differences between different gases in spiderweb plots illustrate materials selectivity as a powerful mapping approach for monitoring selectivity in various gases. Continuous monitoring in 80 ppm methanol yielded stable sensor response for more than 200 h. This comprehensive study illustrates the use of a nanoparticle engineering approach for sensitive, selective and stable gas sensing applications.

Electrical Transport Ability of Nanostructured Potassium-Doped Titanium Oxide Film

Science.gov (United States)

Lee, So-Yoon; Matsuno, Ryosuke; Ishihara, Kazuhiko; Takai, Madoka

2011-02-01

Potassium-doped nanostructured titanium oxide films were fabricated using a wet corrosion process with various KOH solutions. The doped condition of potassium in TiO2 was confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). Nanotubular were synthesized at a dopant concentration of 0.27%, these structures disappeared. To investigate the electrical properties of K-doped TiO2, pseudo metal-oxide-semiconductor field-effect transistor (MOSFET) samples were fabricated. The samples exhibited a distinct electrical behavior and p-type characteristics. The electrical behavior was governed by the volume of the dopant when the dopant concentration was 0.18%.

Spatially resolved analysis of resistive switching in transition metal oxide thin films

OpenAIRE

Landrock, Ruth Christine

2011-01-01

The quest for a non-volatile, small and fast computer memory calls for new memory concepts. Resistive Random Access Memory (ReRAM) based on transition metal oxides is an attractive candidate for future computer memories, because it has the potential of a low power consumption combined with fast switching speeds and good scalability. While in general, switching in such systems relies on a local redox reaction, many details are still unknown or under intense discussion. Especially the geometric...

Transition-metal-doped group-IV monochalcogenides: a combination of two-dimensional triferroics and diluted magnetic semiconductors

Science.gov (United States)

Yang, Liu; Wu, Menghao; Yao, Kailun

2018-05-01

We report the first-principles evidence of a series of two-dimensional triferroics (ferromagnetic + ferroelectric + ferroelastic), which can be obtained by doping transition-metal ions in group-IV monochalcogenide (SnS, SnSe, GeS, GeSe) monolayers, noting that a ferromagnetic Fe-doped SnS2 monolayer has recently been realized (Li B et al 2017 Nat. Commun. 8 1958). The ferroelectricity, ferroelasticity and ferromagnetism can be coupled and the magnetization direction may be switched upon ferroelectric/ferroelastic switching, rendering electrical writing + magnetic reading possible. They can be also two-dimensional half-metals or diluted magnetic semiconductors, where p/n channels or even multiferroic tunneling junctions can be designed by variation in doping and incorporated into a monolayer wafer.

Nanostructured silicon ferromagnet collected by a permanent neodymium magnet.

Science.gov (United States)

Okuno, Takahisa; Thürmer, Stephan; Kanoh, Hirofumi

2017-11-30

Nanostructured silicon (N-Si) was prepared by anodic electroetching of p-type silicon wafers. The obtained magnetic particles were separated by a permanent neodymium magnet as a magnetic nanostructured silicon (mN-Si). The N-Si and mN-Si exhibited different magnetic properties: the N-Si exhibited ferromagnetic-like behaviour, whereas the mN-Si exhibited superparamagnetic-like behaviour.

Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

International Nuclear Information System (INIS)

Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; Kim, Minu; Kang, Tae Dong

2017-01-01

Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering by largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2– ), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.

DNA nanostructure-directed assembly of metal nanoparticle superlattices

Science.gov (United States)

Julin, Sofia; Nummelin, Sami; Kostiainen, Mauri A.; Linko, Veikko

2018-05-01

Structural DNA nanotechnology provides unique, well-controlled, versatile, and highly addressable motifs and templates for assembling materials at the nanoscale. These methods to build from the bottom-up using DNA as a construction material are based on programmable and fully predictable Watson-Crick base pairing. Researchers have adopted these techniques to an increasing extent for creating numerous DNA nanostructures for a variety of uses ranging from nanoelectronics to drug-delivery applications. Recently, an increasing effort has been put into attaching nanoparticles (the size range of 1-20 nm) to the accurate DNA motifs and into creating metallic nanostructures (typically 20-100 nm) using designer DNA nanoshapes as molds or stencils. By combining nanoparticles with the superior addressability of DNA-based scaffolds, it is possible to form well-ordered materials with intriguing and completely new optical, plasmonic, electronic, and magnetic properties. This focused review discusses the DNA structure-directed nanoparticle assemblies covering the wide range of different one-, two-, and three-dimensional systems.

Decontamination of aqueous effluents containing metallic cations or anions by iron oxides under the action of a magnetic field

International Nuclear Information System (INIS)

Goncalves, M. A.; Camilo, R. L.; Cohen, V. H.; Yamaura, M.

1999-01-01

This work deals with a review of decontamination processes of aqueous effluents containing metallic cations and anions by using iron oxides as adsorber. Conditions to obtain the different iron oxides and adsorption capacities for cations and anions are presented and precipitation and/or adsorption mechanisms studies under the point of view of oxide-interface phenomena are described. Emphasis will be applied to the magnetite combined with inorganic exchanger or liquid extractants which magnetic properties has been used to enhance metals removal. Experimental results of a synthetic magnetite production and its adsorption capacity as a function of a magnetic field intensity are also showed. (authors)

Morphological transition of ZnO nanostructures influenced by magnesium doping

International Nuclear Information System (INIS)

Premkumar, T.; Zhou, Y.S.; Gao, Y.; Baskar, K.; Jiang, L.; Lu, Y.F.

2012-01-01

Wurtzite zinc oxide (ZnO) nanochains have been synthesized through high-pressure pulsed laser deposition. The chain-like ZnO nanostructures were obtained from magnesium (Mg) doped ZnO targets, whereas vertically aligned nanorods were obtained from primitive ZnO targets. The Mg doping has influenced the morphological transition of ZnO nanostructures from nanorods to nanochains. The field emission scanning electron microscope images revealed the growth of beaded ZnO nanochains. The ZnO nanochains of different diameters 40 and 120 nm were obtained. The corresponding micro-Raman spectra showed strong E 2H mode of ZnO, which confirmed the good crystallinity of the nanochains. In addition to near band edge emission at 3.28 eV, ZnO nanochains show broad deep level emission at 2.42 eV than that of ZnO nanorods.

Understanding of catalysis on early transition metal oxide-based catalysts through exploration of surface structure and chemistry during catalysis using in-situ approaches

Energy Technology Data Exchange (ETDEWEB)

Tao, Franklin [Univ. of Kansas, Lawrence, KS (United States). Dept. of Chemical and Petroleum Engineering. Dept. of Chemistry

2015-09-14

Two main categories of heterogeneous catalysts are metal and metal oxide which catalyze 80% chemical reactions at solid-gas and solid-liquid interfaces. Metal oxide catalysts are much more complicated than metal catalysts. The reason is that the cations of the metal atoms could exhibit a few different oxidation states on surface of the same catalyst particle such as Co₃O₄ or change of their oxidation states under different reactive environments. For a metal catalyst, there is only one oxidation state typically. In addition, surface of a metal oxide can be terminated with multiple surface functionalities including O atoms with different binding configurations and OH group. For metal, only metal atoms are exposed typically. Obviously, the complication of surface chemistry and structure of a metal oxide makes studies of surface of an oxide catalyst very challenging. Due to the complication of surface of a meal oxide, the electronic and geometric structures of surface of a metal oxide and the exposed species have received enormous attention since oxide catalysts catalyze at least 1/3 chemical reactions in chemical and energy industries. Understanding of catalytic reactions on early transition metal oxide-based catalysts is fundamentally intriguing and of great practical interest in energy- and environment-related catalysis. Exploration of surface chemistry of oxide-based catalysts at molecular level during catalysis has remained challenging though it is critical in deeply understanding catalysis on oxide-based catalysts and developing oxide-based catalysts with high activity and selectivity. Thus, the overall objective of this project is to explore surface chemistry and structure of early transition metal oxide-based catalysts through in-situ characterization of surface of catalysts, measurements of catalytic performances, and then build an intrinsic correlation of surface chemistry and structure with their catalytic performances in a few

Metal oxide nanorod arrays on monolithic substrates

Energy Technology Data Exchange (ETDEWEB)

Gao, Pu-Xian; Guo, Yanbing; Ren, Zheng

2018-01-02

A metal oxide nanorod array structure according to embodiments disclosed herein includes a monolithic substrate having a surface and multiple channels, an interface layer bonded to the surface of the substrate, and a metal oxide nanorod array coupled to the substrate surface via the interface layer. The metal oxide can include ceria, zinc oxide, tin oxide, alumina, zirconia, cobalt oxide, and gallium oxide. The substrate can include a glass substrate, a plastic substrate, a silicon substrate, a ceramic monolith, and a stainless steel monolith. The ceramic can include cordierite, alumina, tin oxide, and titania. The nanorod array structure can include a perovskite shell, such as a lanthanum-based transition metal oxide, or a metal oxide shell, such as ceria, zinc oxide, tin oxide, alumina, zirconia, cobalt oxide, and gallium oxide, or a coating of metal particles, such as platinum, gold, palladium, rhodium, and ruthenium, over each metal oxide nanorod. Structures can be bonded to the surface of a substrate and resist erosion if exposed to high velocity flow rates.

Nanostructured tungsten trioxide thin films synthesized for photoelectrocatalytic water oxidation: a review.

Science.gov (United States)

Zhu, Tao; Chong, Meng Nan; Chan, Eng Seng

2014-11-01

The recent developments of nanostructured WO3 thin films synthesized through the electrochemical route of electrochemical anodization and cathodic electrodeposition for the application in photoelectrochemical (PEC) water splitting are reviewed. The key fundamental reaction mechanisms of electrochemical anodization and cathodic electrodeposition methods for synthesizing nanostructured WO3 thin films are explained. In addition, the effects of metal oxide precursors, electrode substrates, applied potentials and current densities, and annealing temperatures on size, composition, and thickness of the electrochemically synthesized nanostructured WO3 thin films are elucidated in detail. Finally, a summary is given for the general evaluation practices used to calculate the energy conversion efficiency of nanostructured WO3 thin films and a recommendation is provided to standardize the presentation of research results in the field to allow for easy comparison of reported PEC efficiencies in the near future. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Metal-insulator transition in vanadium dioxide

International Nuclear Information System (INIS)

Zylbersztejn, A.; Mott, N.F.

1975-01-01

The basic physical parameters which govern the metal-insulator transition in vanadium dioxide are determined through a review of the properties of this material. The major importance of the Hubbard intra-atomic correlation energy in determining the insulating phase, which was already evidence by studies of the magnetic properties of V 1 -/subx/Cr/subx/O 2 alloys, is further demonstrated from an analysis of their electrical properties. An analysis of the magnetic susceptibility of niobium-doped VO 2 yields a picture for the current carrier in the low-temperature phase in which it is accompanied by a spin cloud (owing to Hund's-rule coupling), and has therefore an enhanced mass (m approx. = 60m 0 ). Semiconducting vanadium dioxide turns out to be a borderline case for a classical band-transport description; in the alloys at high doping levels, Anderson localization with hopping transport can take place. Whereas it is shown that the insulating phase cannot be described correctly without taking into account the Hubbard correlation energy, we find that the properties of the metallic phase are mainly determined by the band structure. Metallic VO 2 is, in our view, similar to transition metals like Pt or Pd: electrons in a comparatively wide band screening out the interaction between the electrons in a narrow overlapping band. The magnetic susceptibility is described as exchange enhanced. The large density of states at the Fermi level yields a substantial contribution of the entropy of the metallic electrons to the latent heat. The crystalline distortion removes the band degeneracy so that the correlation energy becomes comparable with the band width and a metal-insulator transition takes place

Engineered Metallic Nanostructures: Fabrication, Characterization, and Applications

Science.gov (United States)

Bohloul, Arash

Metallic nanostructures have garnered a great deal of attention due to their fascinating optical properties, which differ from the bulk metal. They have been proven to exceed expectations in wide variety of applications including chemical and biological sensing. Nevertheless, high-throughput and low cost nanofabrication techniques are required to implant metallic nanostructures in widespread applications. With that vision, this thesis presents a versatile and reliable method for scalable fabrication of gold nanostructures. In this approach, a plasma-treated ordered array of polystyrene nanospheres acts as an initial mask. The key step in this process is the vapor-deposition of nickel as a sacrificial mask. Thereby, gold nanostructures are directly formed on the substrate through the nickel mask. This is an easy, powerful, and straightforward method that offers several degrees of freedom to precisely control the shape and size of nanostructures. We made a library of nanostructures including gold nanocrescents, double crescents, nanorings, and nanodisks with the ability to tune the size in the range of 150 to 650 nm. The fabricated nanostructures are highly packed and uniformly cover the centimeter scale substrate. The optical properties of metallic nanostructures were extensively studied by a combination of UV-Vis-NIR and Fourier transform infrared (FTIR) spectroscopies, and correlation between optical response and geometrical parameters were investigated. In the next part of this thesis, highly sensitive surface enhanced infrared absorption (SEIRA) analysis was demonstrated on gold nanocrescent arrays. Theoretical modeling was confirmed that these substrates provide highly dense and strong hot-spots over the substrate, which is required for surface enhanced spectroscopic studies. Gold nanocrescent arrays exhibit highly tunable plasmon resonance to cover desired molecular vibrational bands. These substrates experimentally illustrated 3 orders of magnitude

Modelling study of magnetic and concentration phase transition in ultrathin antiferromagnetic films

International Nuclear Information System (INIS)

Leonid, Afremov; Aleksandr, Petrov

2014-01-01

Using the method of the ''average spin'' a modelling study of magnetic and concentration phase transition in ultrathin antiferromagnetic of different crystalline structure has been carried out. It has been shown, that relative change of Neel temperature is subject to the power law with negative index which doesn't depend on the film's crystal kind. The calculation of the dependence of phase transition critical concentration in diluted magnetic material on the film thickness has been made out. The legitimacy of the use of the method developed for modelling of magnetic and concentration phase transition in different nanostructures is certified by accordance between the results of calculations and the experimental data

Manipulating Light with Transition Metal Clusters, Organic Dyes, and Metal Organic Frameworks

Energy Technology Data Exchange (ETDEWEB)

Ogut, Serdar [Univ. of Illinois, Chicago, IL (United States)

2017-09-11

The primary goals of our research program is to develop and apply state-of-the-art first-principles methods to predict electronic and optical properties of three systems of significant scientific and technological interest: transition metal clusters, organic dyes, and metal-organic frameworks. These systems offer great opportunities to manipulate light for a wide ranging list of energy-related scientific problems and applications. During this grant period, we focused our investigations on the development, implementation, and benchmarking of many-body Green’s function methods (GW approximation and the Bethe-Salpeter equation) to examine excited-state properties of transition metal/transition-metal-oxide clusters and organic molecules that comprise the building blocks of dyes and metal-organic frameworks.

An efficient magnetic tight-binding method for transition metals and alloys

DEFF Research Database (Denmark)

Barreteau, Cyrille; Spanjaard, Daniel; Desjonquères, Marie-Catherine

2016-01-01

that does not necessitate any further fitting is proposed to deal with systems made of several chemical elements. This model is extended to spin (and orbital) polarized materials by adding Stoner-like and spin–orbit interactions. Collinear and non-collinear magnetism as well as spin-spirals are considered......An efficient parameterized self-consistent tight-binding model for transition metals using s, p and d valence atomic orbitals as a basis set is presented. The parameters of our tight-binding model for pure elements are determined from a fit to bulk ab-initio calculations. A very simple procedure...

Nano-Structured Magnesium Oxide Coated Iron Ore: Its Application to the Remediation of Wastewater Containing Lead.

Science.gov (United States)

Nagarajah, Ranjini; Jang, Min; Pichiah, Saravanan; Cho, Jongman; Snyder, Shane A

2015-12-01

Magnetically separable nano-structured magnesium oxide coated iron ore (IO(MgO)) was prepared using environmentally benign chemicals, such as iron ore (IO), magnesium(II) nitrate hexahydrate [Mg(NO3)2 x 6H2O] and urea; via an easy and fast preparation method. The lO(MgO) was characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) and alternating gradient magnetometer (AGM) analyses. The isotherm and kinetic studies indicated that lO(MgO) has a comparably higher Langmuir constant (K(L), 1.69 L mg(-1)) and maximum sorption capacity (33.9 mg g(-1)) for lead (Pb) than other inorganic media. Based on MgO amount, the removal capacity of Pb by IO(MgO) was 2,724 mg Pb (g MgO)(-1), which was higher than that (1,980 mg g(-1)) for flowerlike magnesium oxide nanostructures reported by Cao et al. The kinetics, FE-SEM, elemental mapping and XRD results revealed that the substitution followed by precipitation was identified as the mechanism of Pb removal and plumbophyllite (Pb2Si4O10 x H2O) was the precipitated phase of Pb. A leaching test revealed that IOMgO) had negligible concentrations of leached Fe at pH 4-9. Since the base material, IO, is cheap and easily available, lO(MgO) could be produced in massive amounts and used for remediation of wastewater containing heavy metals, applying simple and fast magnetic separation.

Point-contact spectroscopy of unsaturated transition-metal oxides and the problem of zero-bias anomalies

International Nuclear Information System (INIS)

Tulina, N.A.

1985-01-01

The point-contact spectra of oxides with metallic conductivity WO 2 , ReO 3 , and MoO 2 are studied. It is shown that the zero-bias anomalies, which are often observed in the spectra of transition metals, are determined by the presence of an interlayer consisting of an oxide of the above type in the region of the point contact. Zero-bias anomalies do not occur in the point-contact spectra of Zn--MoO 2 -chip heterocontacts. In the studies of such heterocontacts the major maxima in the electron--phonon interaction of MoO 2 were determined at the energies hω/sub T/Aapprox.28 meV and hω/sub L/Aapprox.41 meV

Base-Free Selective Oxidation of Glycerol over LDH Hosted Transition Metal Complexes Using 3% H2O2 as Oxidant

Directory of Open Access Journals (Sweden)

Xiaoli Wang

2016-07-01

Full Text Available A series of transition metal sulphonato-Schiff base complexes were intercalated into Mg–Al layered-double hydroxides (LDHs. The obtained catalysts were characterized by FTIR, XRD, N2 sorption, SEM and elemental analysis, and then were used in the selective oxidation of glycerol (GLY using 3% H2O2 as an oxidant. It was found that their catalytic performances were closely related to the loading of active complexes, the Schiff base ligands and the metal centers of the catalysts, as well as the reaction conditions. The optimal conversion of GLY was 85.0%, while the selectivity of 1,3-dihydroxyacetone (DHA was 56.5%. Moreover, the catalysts could be reused at least 10 times.

Trigonal Prismatic Tris-pyridineoximate Transition Metal Complexes: A Cobalt(II) Compound with High Magnetic Anisotropy.

Science.gov (United States)

Pavlov, Alexander A; Savkina, Svetlana A; Belov, Alexander S; Nelyubina, Yulia V; Efimov, Nikolay N; Voloshin, Yan Z; Novikov, Valentin V

2017-06-19

High magnetic anisotropy is a key property of paramagnetic shift tags, which are mostly studied by NMR spectroscopy, and of single molecule magnets, for which magnetometry is usually used. We successfully employed both these methods in analyzing magnetic properties of a series of transition metal complexes, the so-called clathrochelates. A cobalt complex was found to be both a promising paramagnetic shift tag and a single molecule magnet because of it having large axial magnetic susceptibility tensor anisotropy at room temperature (22.5 × 10 -32 m 3 mol -1 ) and a high effective barrier to magnetization reversal (up to 70.5 cm -1 ). The origin of this large magnetic anisotropy is a negative value of zero-field splitting energy that reaches -86 cm -1 according to magnetometry and NMR measurements.

Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics

Science.gov (United States)

Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M.; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

2018-07-01

All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV–vis spectroscopy and AFM measurements show that this functionality stems from the films’ ability to structurally tune their HOMO–LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures’ plausibility for on-chip molecular electronics operative at room temperature.

Size-dependent single electron transfer and semi-metal-to-insulator transitions in molecular metal oxide electronics.

Science.gov (United States)

Balliou, Angelika; Bouroushian, Mirtat; Douvas, Antonios M; Skoulatakis, George; Kennou, Stella; Glezos, Nikos

2018-07-06

All-inorganic self-arranged molecular transition metal oxide hyperstructures based on polyoxometalate molecules (POMs) are fabricated and tested as electronically tunable components in emerging electronic devices. POM hyperstructures reveal great potential as charging nodes of tunable charging level for molecular memories and as enhancers of interfacial electron/hole injection for photovoltaic stacks. STM, UPS, UV-vis spectroscopy and AFM measurements show that this functionality stems from the films' ability to structurally tune their HOMO-LUMO levels and electron localization length at room temperature. By adapting POM nanocluster size in solution, self-doping and current modulation of four orders of magnitude is monitored on a single nanocluster on SiO 2 at voltages as low as 3 Volt. Structurally driven insulator-to-semi-metal transitions and size-dependent current regulation through single electron tunneling are demonstrated and examined with respect to the stereochemical and electronic structure of the molecular entities. This extends the value of self-assembly as a tool for correlation length and electronic properties tuning and demonstrate POM hyperstructures' plausibility for on-chip molecular electronics operative at room temperature.

Synthesis of magnetic nanofibers using femtosecond laser material processing in air

Directory of Open Access Journals (Sweden)

Tan Bo

2011-01-01

Full Text Available Abstract In this study, we report formation of weblike fibrous nanostructure and nanoparticles of magnetic neodymium-iron-boron (NdFeB via femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Scanning electron microscopy (SEM analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanofibers diameter varies between 30 and 70 nm and they are mixed with nanoparticles. The effect of pulse to pulse separation rate on the size of the magnetic fibrous structure and the magnetic strength was reported. X-ray diffraction (XRD analysis revealed metallic and oxide phases in the nanostructure. The growth of magnetic nanostructure is highly recommended for the applications of magnetic devices like biosensors and the results suggest that the pulsed-laser method is a promising technique for growing nanocrystalline magnetic nanofibers and nanoparticles for biomedical applications.

Synthesis of magnetic nanofibers using femtosecond laser material processing in air

Science.gov (United States)

2011-01-01

In this study, we report formation of weblike fibrous nanostructure and nanoparticles of magnetic neodymium-iron-boron (NdFeB) via femtosecond laser radiation at MHz pulse repetition frequency in air at atmospheric pressure. Scanning electron microscopy (SEM) analysis revealed that the nanostructure is formed due to aggregation of polycrystalline nanoparticles of the respective constituent materials. The nanofibers diameter varies between 30 and 70 nm and they are mixed with nanoparticles. The effect of pulse to pulse separation rate on the size of the magnetic fibrous structure and the magnetic strength was reported. X-ray diffraction (XRD) analysis revealed metallic and oxide phases in the nanostructure. The growth of magnetic nanostructure is highly recommended for the applications of magnetic devices like biosensors and the results suggest that the pulsed-laser method is a promising technique for growing nanocrystalline magnetic nanofibers and nanoparticles for biomedical applications. PMID:21711890

Direct writing of metal nanostructures: lithographic tools for nanoplasmonics research.

Science.gov (United States)

Leggett, Graham J

2011-03-22

Continued progress in the fast-growing field of nanoplasmonics will require the development of new methods for the fabrication of metal nanostructures. Optical lithography provides a continually expanding tool box. Two-photon processes, as demonstrated by Shukla et al. (doi: 10.1021/nn103015g), enable the fabrication of gold nanostructures encapsulated in dielectric material in a simple, direct process and offer the prospect of three-dimensional fabrication. At higher resolution, scanning probe techniques enable nanoparticle particle placement by localized oxidation, and near-field sintering of nanoparticulate films enables direct writing of nanowires. Direct laser "printing" of single gold nanoparticles offers a remarkable capability for the controlled fabrication of model structures for fundamental studies, particle-by-particle. Optical methods continue to provide a powerful support for research into metamaterials.

Correlations in rare-earth transition-metal permanent magnets

International Nuclear Information System (INIS)

Skomski, R.; Manchanda, P.; Kashyap, A.

2015-01-01

It is investigated how electron-electron correlations affect the intrinsic properties of rare-earth transition-metal magnets. Focusing on orbital moment and anisotropy, we perform model calculations for 3d-4f alloys and density-functional theory (DFT) calculations for NdCo 5 . On an independent-electron level, the use of a single Slater determinant with broken spin symmetry introduces Hund's rule correlations, which govern the behavior of rare-earth ions and of alloys described by the local spin density approximation (LSDA) and LSDA + U approximations to DFT. By contrast, rare-earth ions in intermetallics involve configuration interactions between two or more Slater determinants and lead to phenomena such as spin-charge distribution. Analyzing DFT as a Legendre transformation and using Bethe's crystal-field theory, we show that the corresponding density functionals are very different from familiar LSDA-type expressions and outline the effect of spin-charge separation on the magnetocrystalline anisotropy

Correlations in rare-earth transition-metal permanent magnets

Science.gov (United States)

Skomski, R.; Manchanda, P.; Kashyap, A.

2015-05-01

It is investigated how electron-electron correlations affect the intrinsic properties of rare-earth transition-metal magnets. Focusing on orbital moment and anisotropy, we perform model calculations for 3d-4f alloys and density-functional theory (DFT) calculations for NdCo5. On an independent-electron level, the use of a single Slater determinant with broken spin symmetry introduces Hund's rule correlations, which govern the behavior of rare-earth ions and of alloys described by the local spin density approximation (LSDA) and LSDA + U approximations to DFT. By contrast, rare-earth ions in intermetallics involve configuration interactions between two or more Slater determinants and lead to phenomena such as spin-charge distribution. Analyzing DFT as a Legendre transformation and using Bethe's crystal-field theory, we show that the corresponding density functionals are very different from familiar LSDA-type expressions and outline the effect of spin-charge separation on the magnetocrystalline anisotropy.

Metal films with imprinted nanostructures by template stripping

DEFF Research Database (Denmark)

Eriksen, René Lynge; Pors, Anders; Dreier, Jes

We present a novel template stripping procedure for fabricating metal films with imprinted nanostructures. The basic idea is to deposit a gold film onto a nano-structured substrate and subsequently strip the film from the substrate surface thereby revealing imprinted nanostructures in the film...... result is a thin gold film with imprinted nano-cavities....

Two-Dimensional Transition Metal Oxide and Chalcogenide-Based Photocatalysts

Science.gov (United States)

Haque, Farjana; Daeneke, Torben; Kalantar-zadeh, Kourosh; Ou, Jian Zhen

2018-06-01

Two-dimensional (2D) transition metal oxide and chalcogenide (TMO&C)-based photocatalysts have recently attracted significant attention for addressing the current worldwide challenges of energy shortage and environmental pollution. The ultrahigh surface area and unconventional physiochemical, electronic and optical properties of 2D TMO&Cs have been demonstrated to facilitate photocatalytic applications. This review provides a concise overview of properties, synthesis methods and applications of 2D TMO&C-based photocatalysts. Particular attention is paid on the emerging strategies to improve the abilities of light harvesting and photoinduced charge separation for enhancing photocatalytic performances, which include elemental doping, surface functionalization as well as heterojunctions with semiconducting and conductive materials. The future opportunities regarding the research pathways of 2D TMO&C-based photocatalysts are also presented. [Figure not available: see fulltext.

Computational study on the half-metallicity in transition metal—oxide-incorporated 2D g-C3N4 nanosheets

Science.gov (United States)

Gao, Qian; Wang, Hui-Li; Zhang, Li-Fu; Hu, Shuang-Lin; Hu, Zhen-Peng

2018-06-01

In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal-oxide-incorporated 2D g-C3N4 nanosheet (labeled C3N4-TM-O, TM = Sc-Mn). The results suggest that the TM-O binds to g-C3N4 nanosheets strongly for all systems. We found that the 2D C3N4-TM-O framework is ferromagnetic for TM = Sc, Ti, V, Cr, while it is antiferromagnetic for TM = Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures ( T c ) of the C3N4-TM-O (TM = Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C3N4 nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C3N4 nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.

Mechanochemical synthesis of graphene oxide-supported transition metal catalysts for the oxidation of isoeugenol to vanillin

Directory of Open Access Journals (Sweden)

Ana Franco

2017-07-01

Full Text Available Vanillin is one of the most commonly used natural products, which can also be produced from lignin-derived feedstocks. The chemical synthesis of vanillin is well-established in large-scale production from petrochemical-based starting materials. To overcome this problem, lignin-derived monomers (such as eugenol, isoeugenol, ferulic acid etc. have been effectively used in the past few years. However, selective and efficient production of vanillin from these feedstocks still remains an issue to replace the existing process. In this work, new transition metal-based catalysts were proposed to investigate their efficiency in vanillin production. Reduced graphene oxide supported Fe and Co catalysts showed high conversion of isoeugenol under mild reaction conditions using H2O2 as oxidizing agent. Fe catalysts were more selective as compared to Co catalysts, providing a 63% vanillin selectivity at 61% conversion in 2 h. The mechanochemical process was demonstrated as an effective approach to prepare supported metal catalysts that exhibited high activity for the production of vanillin from isoeugenol.

Modulating the electronic and magnetic properties of bilayer borophene via transition metal atoms intercalation: from metal to half metal and semiconductor.

Science.gov (United States)

Zhang, Xiuyun; Sun, Yi; Ma, Liang; Zhao, Xinli; Yao, Xiaojing

2018-07-27

Borophene, a two-dimensional monolayer made of boron atoms, has attracted wide attention due to its appealing properties. Great efforts have been devoted to fine tuning its electronic and magnetic properties for desired applications. Herein, we theoretically investigate the versatile electronic and magnetic properties of bilayer borophene (BLB) intercalated by 3d transition metal (TM) atoms, TM@BLBs (TM = Ti-Fe), using ab initio calculations. Four allotropes of AA-stacking (α 1 -, β-, β 12 - and χ 3 -) BLBs with different intercalation concentrations of TM atoms are considered. Our results show that the TM atoms are strongly bonded to the borophene layers with fairly large binding energies, around 6.31 ∼ 15.44 eV per TM atom. The BLBs with Cr and Mn intercalation have robust ferromagnetism, while for the systems decorated with Fe atoms, fruitful magnetic properties, such as nonmagnetic, ferromagnetic or antiferromagnetic, are identified. In particular, the α 1 - and β-BLBs intercalated by Mn or Fe atom can be transformed into a semiconductor, half metal or graphene-like semimetal. Moreover, some heavily doped TM@BLBs expose high Curie temperatures above room temperature. The attractive properties of TM@BLBs entail an efficient way to modulate the electronic and magnetic properties of borophene sheets for advanced applications.

Technologies for deposition of transition metal oxide thin films: application as functional layers in “Smart windows” and photocatalytic systems

Science.gov (United States)

Gesheva, K.; Ivanova, T.; Bodurov, G.; Szilágyi, I. M.; Justh, N.; Kéri, O.; Boyadjiev, S.; Nagy, D.; Aleksandrova, M.

2016-02-01

“Smart windows” are envisaged for future low-energy, high-efficient architectural buildings, as well as for the car industry. By switching from coloured to fully bleached state, these windows regulate the energy of solar flux entering the interior. Functional layers in these devices are the transition metals oxides. The materials (transitional metal oxides) used in smart windows can be also applied as photoelectrodes in water splitting photocells for hydrogen production or as photocatalytic materials for self-cleaning surfaces, waste water treatment and pollution removal. Solar energy utilization is recently in the main scope of numerous world research laboratories and energy organizations, working on protection against conventional fuel exhaustion. The paper presents results from research on transition metal oxide thin films, fabricated by different methods - atomic layer deposition, atmospheric pressure chemical vapour deposition, physical vapour deposition, and wet chemical methods, suitable for flowthrough production process. The lower price of the chemical deposition processes is especially important when the method is related to large-scale glazing applications. Conclusions are derived about which processes are recently considered as most prospective, related to electrochromic materials and devices manufacturing.

Technologies for deposition of transition metal oxide thin films: application as functional layers in “Smart windows” and photocatalytic systems

International Nuclear Information System (INIS)

Gesheva, K; Ivanova, T; Bodurov, G; Szilágyi, I M; Justh, N; Kéri, O; Boyadjiev, S; Nagy, D; Aleksandrova, M

2016-01-01

“Smart windows” are envisaged for future low-energy, high-efficient architectural buildings, as well as for the car industry. By switching from coloured to fully bleached state, these windows regulate the energy of solar flux entering the interior. Functional layers in these devices are the transition metals oxides. The materials (transitional metal oxides) used in smart windows can be also applied as photoelectrodes in water splitting photocells for hydrogen production or as photocatalytic materials for self-cleaning surfaces, waste water treatment and pollution removal. Solar energy utilization is recently in the main scope of numerous world research laboratories and energy organizations, working on protection against conventional fuel exhaustion. The paper presents results from research on transition metal oxide thin films, fabricated by different methods - atomic layer deposition, atmospheric pressure chemical vapour deposition, physical vapour deposition, and wet chemical methods, suitable for flowthrough production process. The lower price of the chemical deposition processes is especially important when the method is related to large-scale glazing applications. Conclusions are derived about which processes are recently considered as most prospective, related to electrochromic materials and devices manufacturing. (paper)

First-principles data-driven discovery of transition metal oxides for artificial photosynthesis

Science.gov (United States)

Yan, Qimin

We develop a first-principles data-driven approach for rapid identification of transition metal oxide (TMO) light absorbers and photocatalysts for artificial photosynthesis using the Materials Project. Initially focusing on Cr, V, and Mn-based ternary TMOs in the database, we design a broadly-applicable multiple-layer screening workflow automating density functional theory (DFT) and hybrid functional calculations of bulk and surface electronic and magnetic structures. We further assess the electrochemical stability of TMOs in aqueous environments from computed Pourbaix diagrams. Several promising earth-abundant low band-gap TMO compounds with desirable band edge energies and electrochemical stability are identified by our computational efforts and then synergistically evaluated using high-throughput synthesis and photoelectrochemical screening techniques by our experimental collaborators at Caltech. Our joint theory-experiment effort has successfully identified new earth-abundant copper and manganese vanadate complex oxides that meet highly demanding requirements for photoanodes, substantially expanding the known space of such materials. By integrating theory and experiment, we validate our approach and develop important new insights into structure-property relationships for TMOs for oxygen evolution photocatalysts, paving the way for use of first-principles data-driven techniques in future applications. This work is supported by the Materials Project Predictive Modeling Center and the Joint Center for Artificial Photosynthesis through the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, under Contract No. DE-AC02-05CH11231. Computational resources also provided by the Department of Energy through the National Energy Supercomputing Center.

A Versatile Route for the Synthesis of Nickel Oxide Nanostructures Without Organics at Low Temperature

Directory of Open Access Journals (Sweden)

Shah MA

2008-01-01

Full Text Available AbstractNickel oxide nanoparticles and nanoflowers have been synthesized by a soft reaction of nickel powder and water without organics at 100 °C. The mechanism for the formation of nanostructures is briefly described in accordance with decomposition of metal with water giving out hydrogen. The structure, morphology, and the crystalline phase of resulting nanostructures have been characterized by various techniques. Compared with other methods, the present method is simple, fast, economical, template-free, and without organics. In addition, the approach is nontoxic without producing hazardous waste and could be expanded to provide a general and convenient strategy for the synthesis of nanostructures to other functional nanomaterials.

Spin-Orbitronics at Transition Metal Interfaces

KAUST Repository

Manchon, Aurelien

2017-11-09

The presence of large spin–orbit interaction at transition metal interfaces enables the emergence of a variety of fascinating phenomena that have been at the forefront of spintronics research in the past 10 years. The objective of the present chapter is to offer a review of these various effects from a theoretical perspective, with a particular focus on spin transport, chiral magnetism, and their interplay. After a brief description of the orbital hybridization scheme at transition metal interfaces, we address the impact of spin–orbit coupling on the interfacial magnetic configuration, through the celebrated Dzyaloshinskii–Moriya interaction. We then discuss the physics of spin transport and subsequent torques occurring at these interfaces. We particularly address the spin Hall, spin swapping, and inverse spin-galvanic effects. Finally, the interplay between flowing charges and chiral magnetic textures and their induced dynamics are presented. We conclude this chapter by proposing some perspectives on promising research directions.

Spin-Orbitronics at Transition Metal Interfaces

KAUST Repository

Manchon, Aurelien; Belabbes, Abderrezak

2017-01-01

The presence of large spin–orbit interaction at transition metal interfaces enables the emergence of a variety of fascinating phenomena that have been at the forefront of spintronics research in the past 10 years. The objective of the present chapter is to offer a review of these various effects from a theoretical perspective, with a particular focus on spin transport, chiral magnetism, and their interplay. After a brief description of the orbital hybridization scheme at transition metal interfaces, we address the impact of spin–orbit coupling on the interfacial magnetic configuration, through the celebrated Dzyaloshinskii–Moriya interaction. We then discuss the physics of spin transport and subsequent torques occurring at these interfaces. We particularly address the spin Hall, spin swapping, and inverse spin-galvanic effects. Finally, the interplay between flowing charges and chiral magnetic textures and their induced dynamics are presented. We conclude this chapter by proposing some perspectives on promising research directions.

Heavy metal removal from water/wastewater by nanosized metal oxides: A review

International Nuclear Information System (INIS)

Hua, Ming; Zhang, Shujuan; Pan, Bingcai; Zhang, Weiming; Lv, Lu; Zhang, Quanxing

2012-01-01

Nanosized metal oxides (NMOs), including nanosized ferric oxides, manganese oxides, aluminum oxides, titanium oxides, magnesium oxides and cerium oxides, provide high surface area and specific affinity for heavy metal adsorption from aqueous systems. To date, it has become a hot topic to develop new technologies to synthesize NMOs, to evaluate their removal of heavy metals under varying experimental conditions, to reveal the underlying mechanism responsible for metal removal based on modern analytical techniques (XAS, ATR-FT-IR, NMR, etc.) or mathematical models, and to develop metal oxide-based materials of better applicability for practical use (such as granular oxides or composite materials). The present review mainly focuses on NMOs’ preparation, their physicochemical properties, adsorption characteristics and mechanism, as well as their application in heavy metal removal. In addition, porous host supported NMOs are particularly concerned because of their great advantages for practical application as compared to the original NMOs. Also, some magnetic NMOs were included due to their unique separation performance.

Analytical theory of noncollinear amorphous metallic magnetism

International Nuclear Information System (INIS)

Kakehashi, Y.; Uchida, T.

2001-01-01

Analytical theory of noncollinear magnetism in amorphous metals is proposed on the basis of the Gaussian model for the distribution of the interatomic distance and the saddle-point approximation. The theory removes the numerical difficulty in the previous theory based on the Monte-Carlo sampling method, and reasonably describes the magnetic properties of amorphous transition metals

Synchrotron radiation studies of local structure and bonding in transition metal aluminides and rare earth transition metal magnetic nitrides. Final report, August 1, 1990--July 14, 1993

International Nuclear Information System (INIS)

Budnick, J.I.; Pease, D.M.

1995-01-01

The following areas of study are reported on: bonding and near neighbor force constants in NiAl, CoAl, FeAl via temperature dependent EXAFS; alloys formed when Fe or Ga is microalloyed into a NiAl matrix; EXAFS studies of nitrided versus non nitrided Y 2 Fe 17 ; and transition metal x-ray spectra as related to magnetic moments

Nanostructured manganese oxide thin films as electrode material for supercapacitors

Science.gov (United States)

Xia, Hui; Lai, Man On; Lu, Li

2011-01-01

Electrochemical capacitors, also called supercapacitors, are alternative energy storage devices, particularly for applications requiring high power densities. Recently, manganese oxides have been extensively evaluated as electrode materials for supercapacitors due to their low cost, environmental benignity, and promising supercapacitive performance. In order to maximize the utilization of manganese oxides as the electrode material for the supercapacitors and improve their supercapacitive performance, the nanostructured manganese oxides have therefore been developed. This paper reviews the synthesis of the nanostructured manganese oxide thin films by different methods and the supercapacitive performance of different nanostructures.

Two-step growth mechanism of supported Co3O4-based sea-urchin like hierarchical nanostructures