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Investigação de ablação a laser no regime de femtossegundo em materiais homogêneos e estruturados; Investigation of the femtosecond laser ablation on homogeneous and structured materials

Nicolodelli, Gustavo
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 31/03/2011 PT
Relevância na Pesquisa
67.50643%
Embora a ablação a laser venha sendo bastante utilizada em materiais em geral, pouco é entendido sobre o comportamento deste processo perto de uma interface separando dois materiais distintos. Neste contexto, o principal objetivo deste trabalho foi realizar um estudo macroscópico e microscópico dos processos que envolvem a ablação a laser em regime de femtossegundos em materiais homogêneos e estruturados. No caso de materiais estruturados, o estudo focou-se em uma situação de interface, na qual ocorrem mudanças nas propriedades de ablação. Baseado nos resultados, nós pretendemos obter subsídios científicos para entender as aplicações da ablação em regime de pulsos ultracurtos para estruturas estratificadas, tais como de dentes, ossos, interface resina-dente, dente-metal, e outras. Diferentes técnicas experimentais foram idealizadas para determinar a progressão da ablação dentro do material e obter dados extraídos da superfície. Utilizando luz espalhada de uma fonte externa, o processo de ablação foi temporalmente monitorado, permitindo determinar a velocidade de ablação em materiais transparentes, assim como perfis típicos de ablação nestes materiais. Em um segundo experimento, nosso estudo permitiu quantificar a variação da geometria de ablação perto de uma interface separando dois materiais distintos. Nossos dados foram suficientes para prever a ocorrência de uma descontinuidade no perfil da ablação entre dois meios: resina A e resina B...

Materiais estruturados: qual o seu papel na aprendizágem dos primeiros números?

Pinto, Sílvia Isabel Cardoso Lima
Fonte: Instituto Politécnico de Lisboa Publicador: Instituto Politécnico de Lisboa
Tipo: Dissertação de Mestrado
Publicado em /12/2012 POR
Relevância na Pesquisa
47.60763%
Dissertação apresentada para obtenção do grau de Mestre em Educação Matemática na Educação Pré-Escolar e no 1.º e 2.º Ciclos do Ensino Básico; O presente estudo centra-se na importância da utilização de materiais estruturados na aprendizagem dos primeiros números, no âmbito do desenvolvimento do sentido de número. Este estudo tem como objectivo central entender o papel da utilização de materiais estruturados na aprendizagem dos primeiros números, por parte de alunos de 1.º ano. A par deste objectivo pretende-se dar resposta acerca das relações numéricas que emergem da utilização dos materiais (colar de contas, moldura do dez e ábaco horizontal) e entender de que modo estes intervêm na estruturação do processo de cálculo. De acordo com o objectivo do estudo, a investigação adopta uma natureza particularista, descritiva e interpretativa, tendo optado por uma abordagem de tipo qualitativo, sendo que o objecto de análise incide em três pares de alunos de uma turma de 1.º ano. Devido à pretensão de realizar o estudo em contexto natural, a recolha de dados foi feita numa escola, recorrendo a mais que uma técnica, para que se pudesse efectuar, posteriormente, a triangulação de dados. Utilizou-se a observação participante...

Relatório Final da Prática de Ensino Supervisionada O dia-a-dia da Matemática: A importância dos materiais manipuláveis em sala de aula

Duarte, Madalena Filipa Garrido
Fonte: Repositório Comum de Portugal Publicador: Repositório Comum de Portugal
Tipo: Dissertação de Mestrado
Publicado em 22/04/2015 POR
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37.134507%
O presente relatório insere-se no âmbito da Prática Pedagógica Supervisionada do Mestrado de Qualificação para a Docência em Educação Pré-Escolar e Ensino do 1.º Ciclo do Ensino Básico, e pretende refletir sobre a prática desenvolvida ao longo da prática pedagógica decorrida em três semestres, assim como analisar a evolução dos grupos perante a temática abordada. A matemática ao assumir um papel importante no percurso escolar de cada aluno, permite desenvolver capacidades e competências que lhe serão úteis no futuro. Contudo, as crianças e alunos tendem a rejeitar a matemática, o que condiciona o seu envolvimento nas atividades matemáticas e na atribuição de sentidos às aprendizagens matemáticas. Desta forma, o recurso a materiais manipuláveis, estruturados e não estruturados, poderá ser um facilitador na apropriação de conhecimentos matemáticos e no desenvolvimento de capacidades e competências (matemáticas). Esta investigação encontra-se sustentada por um design de investigação-ação, do paradigma interpretativo, através da qual se pretende observar, planificar, refletir, intervir e voltar a refletir consoante os objetivos a alcançar. Deste modo, os instrumentos utilizados são diversos como sejam a observação...

Nano-structured alloy and composite coatings for high temperature applications

Gao,Wei; Li,Zhengwei
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2004 EN
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47.39409%
Nano-structured materials often possess special properties that materials with identical compositions but ordinary grain size do not have. This paper reports our work on the surface nano-crystallisation and nano-structured alloy and composite coatings. A number of processing methods including magnetron sputtering, thermal spray and pulse electro-spark deposition have been used to produce surface nano-crystalline structure. The compositions and microstructures can be well controlled by using different targets or electrodes, nano-structured composites and adjusting processing parameters. Surface nano-structured coatings can provide special chemical, mechanical and electronic properties such as high temperature corrosion and corrosive wear resistance. It has potential applications such as turbine blades, engine parts for petrochemical, aerospace and electronic device industries. This paper is focused on the study of the interrelations between processing, microstructure and properties. Physical models have been established to explain the effects of nano-crystalline structure on the properties.

Preparation and Characterization of Nano structured Materials from Fly Ash: A Waste from Thermal Power Stations, by High Energy Ball Milling

Paul, K Thomas; Satpathy, SK; Manna, I; Chakraborty, KK; Nando, GB
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 11/07/2007 EN
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36.976477%
The Class F fly ash has been subjected to high energy ball milling and has been converted into nanostructured material. The nano structured fly ash has been characterized for its particle size by using particle size analyzer, specific surface area with the help of BET surface area apparatus, structure by X-ray diffraction studies and FTIR, SEM and TEM have been used to study particle aggregation and shape of the particles. On ball milling, the particle size got reduced from 60 μm to 148 nm by 405 times and the surface area increased from 0.249 m2/gm to 25.53 m2/gm i.e. by more than 100%. Measurement of surface free energy as well as work of adhesion found that it increased with increased duration of ball milling. The crystallite was reduced from 36.22 nm to 23.01 nm for quartz and from 33.72 nm to 16.38 nm for mullite during ball milling to 60 h. % crystallinity reduced from 35% to 16% during 60 h of ball milling because of destruction of quartz and hematite crystals and the nano structured fly ash is found to be more amorphous. Surface of the nano structured fly ash has become more active as is evident from the FTIR studies. Morphological studies revealed that the surface of the nano structured fly ash is more uneven and rough and shape is irregular...

D,L-Cyclic Peptides as Structural Materials

Rubin, Daniel James
Fonte: Harvard University Publicador: Harvard University
Tipo: Thesis or Dissertation; text Formato: application/pdf
EN
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46.9069%
The bioengineer has a choice of building with proteins, peptides, polymers, nucleic acids, lipids, metals and minerals, each class containing tremendous diversity within its category. While the platforms are diverse, they can be unified by a common goal: to engineer nano- and micro-scale order to improve functionality. In doing so, self-assembling systems aim to bring the lessons learned from the order in natural systems83 into the therapeutics, materials, and electronics that society uses every day. The rigid geometry and tunable chemistry of D,L-cyclic peptides make them an intriguing building-block for the rational design of nano- and microscale hierarchically structured materials. Herein, we utilize a combination of electron microscopy, nanomechanical characterization including depth sensing-based bending experiments, and molecular modeling methods to obtain the structural and mechanical characteristics of cyclo-[(Gln-D-Leu)4] (QL4) assemblies. QL4 monomers assemble to form large, rod-like structures with diameters up to 2 μm and lengths of 10s to 100s of μm. Image analysis suggests that large assemblies are hierarchically organized from individual tubes that undergo bundling to form larger structures. With an elastic modulus of 11.3 ± 3.3 GPa...

Breaking symmetries in ordered materials : spin polarized light transport in magnetized noncentrosymmetric 1D photonic crystals, and photonic gaps and fabrication of quasiperiodic structured materials from interference lithography

Bita, Ion
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 219 leaves
ENG
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67.387275%
Effects of breaking various symmetries on optical properties in ordered materials have been studied. Photonic crystals lacking space-inversion and time-reversal symmetries were shown to display nonreciprocal dispersion relations, and to exhibit a remarkable set of symmetry-related properties. Even in 1D, these materials are found to display indirect photonic band gaps, backward wave propagating modes (antiparallel phase and group velocities) which enable negative refraction at the air-crystal interface, ability to allow bending light with perpendicular magnetic fields, unidirectional superprism effects, etc. By calculating the complex photonic band structure, we show that the gap modes differ fundamentally from the commonly assumed evanescent modes with purely imaginary wave vectors - solely due to symmetry, we show that the gaps of nonreciprocal photonic crystals have complex wave vectors with both imaginary components and non-zero, frequency dependent real components. This basic finding is further studied in the context of tunneling dynamics, by considering the problem of tunneling time for nonreciprocal photonic band gap barriers (the tunneling wave packet has an energy in the middle of the gap).; (cont.) It was found that the classical Hartman effect (independence of tunneling time on barrier length...

Ultra-lightweight nanorelief networks : photopatterned microframes

Choi, Taeyi
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 153 p.
ENG
Relevância na Pesquisa
37.085112%
Lightweight nano-network structures in polymers have been fabricated and investigated for their mechanical properties. Fabrication techniques via holographic interference lithography and phase mask lithography were implemented for periodic and quasiperiodic bicontinuous polymer-air structures on the submicrometer length scale. For 3D quasiperiodically nanostructured materials, quasicrystalline phase mask lithography utilizing 2D quasiperiodic phase mask was successfully employed. 2D hexagonal arrays of air cylinders in SU8 polymer films and 3D four-beam connected (3- R3m ) and octagonal quasicrystalline SU8 films were fabricated and analyzed in this thesis. For investigating the mechanical properties of various nano-network structures, three different methods of mechanical characterization were applied. Atomic force microscopy with its nanometer scale resolution was adopted to conduct force measurements to probe local elastic properties of the sample. Templated by the light intensity distribution from three-beam interference, the spatial distribution of elastic modulus was observed in the pattern of 2D hexagonal air-cylinder and a uniform SU8 polymer film by AFM nanoindentation. A second method for mechanical characterization, the microtensile tester enabled us to evaluate a symmetry effect on the elastic and plastic properties of the polymer fibers and thin films. Large plastic deformation of 200nm-diameter struts comprising the 3D periodic and quasiperiodic microframes of the normal brittle bulk polymer was discovered and is an example of length-scale dependent mechanical behavior. Crack propagation and energy absorption were guided along the symmetry directions in the periodic structures. However...

Bio-inspired optical components

Walish, Joseph John
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 220 p.
ENG
Relevância na Pesquisa
46.879927%
Guiding electro-magnetic radiation is fundamental to optics. Lenses, mirrors, and photonic crystals all accomplish this task by different routes. Understanding the interaction of light with materials is fundamental to improving and extending optical science and engineering as well as producing novel optical elements. Improvement in this understanding should not only include work to understand the interaction with traditional engineering materials but also should target the understanding of the interaction of electromagnetic radiation with biological structures as millions of years of evolution have sorted out numerous ways to modulate light (e.g. the fish eye or the skin of the octopus). The goal of this thesis work is to fabricate novel optical elements by taking cues from nature and extending the state of the art in light guiding behavior. Here, optical elements are defined as structured materials that guide or direct electromagnetic radiation in a predetermined manner. The work presented in this thesis encompasses biologically inspired tunable multilayer reflectors made from block copolymers and improvements to liquid filled lenses which mimic the human eye.In this thesis a poly(styrene)-poly(2-vinylpyridine) block copolymer was used to create a bio-mimetic...

In situ synthesis and characterization of a hierarchically structured Al₂0₃/Al₃Ti composite; In situ synthesis and characterization of a hierarchically structured Al(2)0(3)/Al(3)Ti composite

Zhu, H.; Jiang, Y.; Song, J.; Li, J.; Munroe, P.; Xie, Z.
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
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37.164233%
A hierarchically structured α-Al₂O₃/Al₃Ti composite was fabricated by an in situ process called exothermic dispersive synthesis from a powder blend of Al and TiO₂. The microstructure of the composite was investigated by X-ray diffraction, scanning electron microscopy, and X-ray energy dispersive spectroscopy. Three transitional phases, specifically TiO, Ti₂O₃, and γ-Al₂O₃, were found to form during the reactive process. Using differential scanning calorimetry, it was found that the reaction between the Al and TiO₂ occurred through three intermediate steps and their corresponding activation energies were 390, 205, and 197 kJ/mol, respectively. Moreover, the reaction rate of the third step was found to be much higher than that of the second step, and the time taken by each reaction step decreased with the increase of the heating rate. The findings are critical to understanding the microstructural development in the synthesis of strong and tough Al₂O₃/Al₃Ti composites.; Heguo Zhu, Yaling Jiang, Jinzhu Song, Jianliang Li, Paul Munroe, Zonghan Xie

Experiments on strongly correlated materials under extreme conditions

PURI, ALESSANDRO
Fonte: La Sapienza Universidade de Roma Publicador: La Sapienza Universidade de Roma
Tipo: Tese de Doutorado
EN
Relevância na Pesquisa
36.9069%
The aim of this work has been to investigate the electronic phase transitions and the electronic dynamic behavior of 'strongly correlated materials'. In particular I will show data of three different classes of materials: iron-based superconductors, topological insulators and spin-crossover (SCO) materials, under conditions that can be considered extreme. Experiments have been performed under a variable DC magnetic field from 0 to 5 T, the temperature range was from 4.2 to 300 K and pressure applied was ranging from 0 to 3 GPa. Experiments were carried out the in the majority of the cases by measuring the DC and the AC magnetic susceptibility, while the last case regarded the infrared spectroscopy. The results of the multi-harmonic magnetic susceptibility experiments on iron based superconductors show: a) in the ‘1111’ NdFeAsO1-0.14F0.14, iron pnictide, the coexistence of a superconducting (Tc = 47 K) and a magnetic phase (Tm = 90 K); b) the superconducting phase in the ‘1111’ iron pnictide exhibits good bulk 3D pinning characteristics with a crossover to a 2D behavior for a Hdc field of 1 T. In fact these systems have a layered crystal structure with alternate superconducting iron-pnictogen active layers and rare earth-oxide spacer layers; c) a superconducting phase (Tc = 10 K) coexisting with a magnetic (Tm = 125 K) phase has been detected also in the ‘11’ FeSe1-xTex iron chalcogenide; d) the superconducting phase in the ‘11’ iron-chalcogenides also exhibits good bulk 3D pinning characteristics at low magnetic fields; e) the comparison between the ‘1111’ NdFeAsO1-0.14F0.14 iron pnictide superconductor and the ‘11’ iron chalcogenide superconductors properties...

A Materials Perspective on Casimir and van der Waals Interactions

Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.; Rodriguez-Lopez, P.; Rodriguez, A. W.; Podgornik, R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/09/2015
Relevância na Pesquisa
36.9069%
Interactions induced by electromagnetic fluctuations, such as van der Waals and Casimir forces, are of universal nature present at any length scale between any types of systems with finite dimensions. Such interactions are important not only for the fundamental science of materials behavior, but also for the design and improvement of micro- and nano-structured devices. In the past decade, many new materials have become available, which has stimulated the need of understanding their dispersive interactions. The field of van der Waals and Casimir forces has experienced an impetus in terms of developing novel theoretical and computational methods to provide new insights in related phenomena. The understanding of such forces has far reaching consequences as it bridges concepts in materials, atomic and molecular physics, condensed matter physics, high energy physics, chemistry and biology. In this review, we summarize major breakthroughs and emphasize the common origin of van der Waals and Casimir interactions. We examine progress related to novel ab initio modeling approaches and their application in various systems, interactions in materials with Dirac-like spectra, force manipulations through nontrivial boundary conditions, and applications of van der Waals forces in organic and biological matter. The outlook of the review is to give the scientific community a materials perspective of van der Waals and Casimir phenomena and stimulate the development of experimental techniques and applications.; Comment: 54 pages...

Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited

Butler, Keith T.; Frost, Jarvist M.; Walsh, Aron
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/12/2014
Relevância na Pesquisa
46.844253%
The application of ferroelectric materials (i.e. solids that exhibit spontaneous electric polarisation) in solar cells has a long and controversial history. This includes the first observations of the anomalous photovoltaic effect (APE) and the bulk photovoltaic effect (BPE). The recent successful application of inorganic and hybrid perovskite structured materials (e.g. BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors can be used in conventional photovoltaic architectures. We review developments in this field, with a particular emphasis on the materials known to display the APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical analysis is complemented with first-principles calculation of the underlying electronic structure. In addition to discussing the implications of a ferroelectric absorber layer, and the solid state theory of polarisation (Berry phase analysis), design principles and opportunities for high-efficiency ferroelectric photovoltaics are presented.

Modeling linear and nonlinear soft ferromagnetic materials

Agramunt Puig, Sebastià
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis Formato: application/pdf
Publicado em //2014 ENG; ENG
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37.013608%
Avui en dia els imants formen part de la nostra vida diària, per exemple són responsables de la majoria de conversió, generació i consum d'energia. En aquestes aplicacions es necessita un control precís dels camps magnètics i de les imantacions dels materials per millorar les aplicacions ja existents o descobrir-ne de noves. Això no podria ser possible sense l'impressionant desenvolupament dels materials magnètics en els últims anys. Més concretament durant el segle passat, s'han obtingut valors extrems d'anisotropia cristal·lina que abasta cinc ordres de magnitud obtenint materials tous (molt poca anisotropia) o durs (alta anisotropia). Els materials ferromagnètics tous són de gran interès, perquè poden guiar i concentrar els camps magnètics, presenten poca histèresi i grans valors de imantació de saturació i susceptibilitat. Aquests materials es troben, per exemple, en electroimants, on un nucli de ferromagnètic tou concentra el camp magnètic o en transformadors elèctrics, motors o generadors en els quals es necessiten poques pèrdues energètiques per histèresi. El gran número de potencials aplicacions o aplicacions ja existents té lloc en diferents escales variant des de molt grans (metres) fins a molt petites (nanòmetres). Una de les aplicacions en l'escala gran és la levitació de superconductors. Aquests últims materials han demostrat presentar levitació estable i passiva sent capaços d'aixecar centenars de kilograms. Utilitzant aquests conceptes...

Optical properties of gyroid structured materials: from photonic crystals to metamaterials

Dolan, James A.; Wilts, Bodo D.; Vignolini, Silvia; Baumberg, Jeremy J.; Steiner, Ullrich; Wilkinson, Timothy D.
Fonte: Wiley Publicador: Wiley
Tipo: Article; accepted version
EN
Relevância na Pesquisa
57.28655%
This is the accepted manuscript version of the article. The final version is available from Wiley via http://dx.doi.org/10.1002/adom.201400333; The gyroid is a continuous and triply periodic cubic morphology which possesses a constant mean curvature surface across a range of volumetric ll fractions. Found in a variety of natural and synthetic systems which form through self-assembly, from buttery wing scales to block copolymers, the gyroid also exhibits an inherent chirality not observed in any other similar morphologies. These unique geometrical properties impart to gyroid structured materials a host of interesting optical properties. Depending on the length scale on which the constituent materials are organised, these properties arise from starkly di erent physical mechanisms (such as a complete photonic band gap for photonic crystals and a greatly depressed plasma frequency for optical metamaterials). This article reviews the theoretical predictions and experimental observations of the optical properties of two fundamental classes of gyroid structured materials: photonic crystals (wavelength scale) and metamaterials (subwavelength scale).; This work was supported by the EPSRC through the Cambridge NanoDTC EP/G037221/1, EP/G060649/1...

Deposition and characterisation of bismuth layer-structured ferroelectric films

Hu, Xiaobing
Fonte: University of Cambridge; Department of Materials Science and Metallurgy Publicador: University of Cambridge; Department of Materials Science and Metallurgy
Tipo: Thesis; Doctoral
EN
Relevância na Pesquisa
37.012195%
Bismuth layer-structured ferroelectrics have been recognised as promising film materials for ferroelectric random access memory application due to their excellent fatigue resistance and other electrical properties. This work deals with the deposition and characterisation of epitaxial and polycrystalline W-doped SrBi2Ta2O9 (SBT) and lanthanide-doped bismuth titanate (BiT) films. SBT and W-doped SBT films were fabricated by pulsed laser deposition (PLD) on platinised silicon substrates. The effects of fabrication temperature and W-doping level on film properties were studied. The crystallinity of SBTW films improved with increasing fabrication temperatures, resulting in enhanced ferroelectric properties and dielectric properties above the fabrication temperature of 750 ?C. Dense ceramic samples of Nd- and Sm-doped BiT (BNdT and BSmT) were successfully fabricated for PLD targets by solid state processing. Highly epitaxially (001)-, (118)-, and (104)-oriented Nd-doped bismuth titanate (BNdT) films were grown by PLD on (001)-, (011)-, and (111)-oriented SrTiO3 (STO) single crystal substrates, respectively. A three-dimensional orientation relationship between films and substrates was derived as: BNdT(001)//STO(001), BNdT[ 110 ]//STO[100]. Films showed strong dependence of structural and ferroelectric properties on the crystal orientation. PLD-grown BSmT films on platinised silicon substrates were studied as a function of fabrication temperature...

Optical properties of gyroid structured materials: from photonic crystals to metamaterials

Dolan, James A.; Wilts, Bodo D.; Vignolini, Silvia; Baumberg, Jeremy J.; Steiner, Ullrich; Wilkinson, Timothy D.
Fonte: Wiley Publicador: Wiley
Tipo: Article; accepted version
EN
Relevância na Pesquisa
57.28655%
This is the accepted manuscript. The final version is available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/adom.201400333/abstract.; The gyroid is a continuous and triply periodic cubic morphology which possesses a constant mean curvature surface across a range of volumetric fill fractions. Found in a variety of natural and synthetic systems which form through self-assembly, from butterfly wing scales to block copolymers, the gyroid also exhibits an inherent chirality not observed in any other similar morphologies. These unique geometrical properties impart to gyroid structured materials a host of interesting optical properties. Depending on the length scale on which the constituent materials are organised, these properties arise from starkly different physical mechanisms (such as a complete photonic band gap for photonic crystals and a greatly depressed plasma frequency for optical metamaterials). This article reviews the theoretical predictions and experimental observations of the optical properties of two fundamental classes of gyroid structured materials: photonic crystals (wavelength scale) and metamaterials (subwavelength scale).; This work was supported by the EPSRC through the Cambridge NanoDTC EP/G037221/1...

Structured Materials for Photoelectrochemical Water Splitting

McKone, James; Lewis, Nathan
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Book Section; PeerReviewed Formato: application/pdf
Publicado em //2013
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Efficient and economical photoelectrochemical water splitting requires innovation on several fronts. Tandem solar absorbers could increase the overall efficiency of a water splitting device, but economic considerations motivate research that employs cheap materials combinations. The need to manage simultaneously light absorption, photogenerated carrier collection, ion transport, catalysis, and gas collection drives efforts toward structuring solar absorber and catalyst materials. This chapter divides the subject of structured solar materials into two principal sections. The first section investigates the motivations, benefits, and drawbacks of structuring materials for photoelectrochemical water splitting. We introduce the fundamental elements of light absorption, photogenerated carrier collection, photovoltage, electrochemical transport, and catalytic behavior. For each of these elements, we discuss the figures of merit, the critical length scales associated with each process and the way in which these length scales must be balanced for efficient generation of solar fuels. This discussion assumes a working knowledge of the fundamentals of semiconductor-liquid junctions; for more details the reader is encouraged to consult review articles. The second section of this chapter reviews recent approaches for generating structured semiconductor light absorbers and structured absorber-catalyst composites. This literature review emphasizes the insights gained in the last six years that are specifically related to photoelectrochemical water splitting...

Design and Characterization of Protein-Based Building Blocks for Self-Assembled Nano-Structured Biomaterials

Kim, Minkyu
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação
Publicado em //2011
Relevância na Pesquisa
37.202686%

This study is focused on designing and characterizing protein-based building blocks in order to construct self-assembled nano-structured biomaterials. In detail, this research aims to: (1) investigate a new class of proteins that possess nanospring behaviors at a single-molecule level, and utilize these proteins along with currently characterized elastomeric proteins as building blocks for nano-structured biomaterials; (2) develop a new method to accurately measure intermolecular interactions of self-assembling two or more arbitrary (poly)peptides, and select some of them which have appropriate tensile strength for crosslinking the proteins to construct elastomeric biomaterials; (3) construct well-defined protein building blocks which are composed of elastomeric proteins terminated with self-oligomerizing crosslinkers, and characterize self-assembled structures created by the building blocks to determine whether the elasticity of proteins at single-molecule level can be maintained.

Primary experimental methods of this research are (1) atomic force microscope (AFM) based single-molecule force spectroscopy (SMFS) that allows us to manipulate single molecules and to obtain their mechanical properties such as elasticity, unfolding and refolding properties...

Compositionally modulated Fermi surfaces, structured diffuse scattering and ternary derivatives of 1T-TaS2

Withers, Raymond; Otero-Diaz, L Carlos; Gomez-Herrero, Adrian; Landa-Canovas, Angel R; Prodan, Albert; van Midden, Herman J. P.; Noren, Lasse
Fonte: Academic Press Publicador: Academic Press
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
37.202686%
Ternary derivatives of 1T-TaS2 have been synthesized and the variation in the highly structured diffuse intensity distributions characteristic of such materials carefully monitored to investigate the effect that such substitution has upon the band structures and Fermi surfaces (FSs) of the materials. Removal of d electrons via the replacement of Ta ions with lower valent transition metal ions leads to a systematic increase in the radii of the characteristic structured diffuse intensity distribution. Extended Hückel tight binding calculations of the FSs of the doped samples are carried out and used to predict possible nesting wave-vectors. The results are in reasonably good agreement with the radii of the experimentally observed diffuse intensity distributions.