RESUMO AULA PASSADA Guias de ondas deluz. Fibras ópticas

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1 RESUMO AULA PASSADA Guias de ondas deluz. Fibras ópticas
RESUMO AULA PASSADA Guias de ondas deluz. Fibras ópticas Diferentes tipos de fibras ópticas: tipo degrau, tipo GRIN Modos de propagação na fibra GRIN, como fazer, vários métodos: troca iônica, CVD, fonte de nêutrons. Lentes Selfoc, comparação com lentes clássicas, algumas aplicações: DVD, endoscópio. Demonstração com GRIN (água+acúcar), lente GRIN natural. Selfoc recentes. Distribuição de temas para apresentação por parte dos alunos. dispoptic 2013

2 Noções sobre estado sólido
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3 Kittel, Charles “Introduction to solid state physics”. Biblioteca IFSC
Rede cristalina Kittel, Charles “Introduction to solid state physics”. Biblioteca IFSC dispoptic 2013

4 Características de planos numa rede
Densidade de átomos por plano Relação de índices dos planos com a separação dispoptic 2013

5 Redes de Bravais dispoptic 2013

6 Rede cristalina = rede + base
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7 Outra forma de representar
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8 Descrição de uma rede Translação R0 = R + m1a1 + m2a2 + m3a3
Vetores primitivos ai dispoptic 2013

9 Célula unitária dispoptic 2013

10 BCC Film BCC dispoptic 2013

11 Cúbico simples ou cúbico de corpo centrado?
CsCl Cúbico simples ou cúbico de corpo centrado? dispoptic 2013

12 FCC - Empacotamento fechado
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13 Cristais dispoptic 2013 O = Octaedro T = Tetraedro Filme NaCl e CaF2

14 NaCl dispoptic 2013 Qual é a base? NaCl

15 Empacotamento fechado
dispoptic 2013 Film HCP

16 O que se sabia até então classicamente
Teorema da restrição cristalográfica: Simetria de rotação de 2da, 3ra, 4ta e 6ta ordem Simetria de translação dispoptic 2013

17 Premio Nobel de Química 1996
Novas estruturas Premio Nobel de Química 1996 (1985) Robert F. Curl, Jr., Rice University, Houston, USA Sir Harry W. Kroto FRS, University of Sussex, Brighton, UK Richard E. Smalley, Rice University, Houston, USA The serendipitous discovery of a third allotropic form in 1985, uncovered a fundamentally different structure of closed carbon cages, which were to become known as fullerenes. This new family of non-planar carbon compounds has generated immense interest within the scientific community in such a short period of time, with thousands of papers published about fullerenes and fullerene-based materials to date. In the early 1970's, the chemistry of unsaturated carbon configurations was studied by a group at the University of Sussex, led by Harry Kroto and David Walton. They developed methods for synthesising long chain polyynes, whose vibration-rotation dynamics were studied by microwave spectroscopy. They then used these observations for molecular radioastronomy. From they studied the long-chained polyynylcyanides, HC5N, HC7N and HC9N. These molecules were detected in the cloud material of the interstellar medium by radioastronomy. These molecules turned out to be produced by red giant stars. In the 1980's a technique was developed by Richard Smalley and Bob Curl at Rice University, Texas. They used laser vaporisation of a suitable target to produce clusters of atoms. Kroto realised that by using a graphite target, that the cluster apparatus would be ideal to probe the formation of carbon chains, and so planned a collaboration between his group at Sussex and the one at Rice. The Sussex/Rice experiment took place in September The technique probed the carbon plasma produced by the laser vaporisation by time-of-flight mass spectrometry. The experiments confirmed that large carbon chain/clusters were being formed. During the experiments it was noted that the peak for the C60 molecule (and to a lesser extent C70) behaved unusually and formed under all conditions as well as exhibiting great stability. The experimental evidence, a strong peak at 720 amu (atomic mass units), indicated that a carbon molecule with sixty carbon atoms was forming, but provided little structural information. The research group concluded after reactivity experiments, that the most likely structure was a spheroidal molecule. Kroto mentioned Fuller's geodesic dome structures, which contained pentagons as well as hexagons. The idea was quickly rationalised as the basis of an icosohedral symmetry closed cage structure. The geodesic and electronic bonding factors in the structure accounted for the stability of the molecule, and it was named after Buckminster Fuller. Fullerenes are closed cage structures. Each carbon atom is bonded to three others and is sp2 hybridised. Hexagonal rings are present but pentagonal rings are required for the cage to close. Mass spectrometry has been widely used to study the fullerenes. There is evidence for species as small as C20+, as well as stable peaks for the cluster ions C2n+ (where 2n>32). Fullerenes which are stable or abundant enough to exist in macroscopic quantities have been studied further using a wide range of physical and spectroscopic methods. C60 and C70 have similar properties, with six reversible, one electron reductions to C606- and C706- having been observed, whereas oxidation is irreversible. The first reduction for both fullerenes is ~1.0 V (Fc/Fc+), indicating they have electron accepting properties. C76 exhibits both electron donor/acceptor properties. C60 has a tendency of avoiding having double bonds within the pentagonal rings which makes electron delocalisation poor, and results in the fact that C60 is not "superaromatic". C60 behaves very much like an electron deficient alkene and readily reacts with electron rich species. Buckminster Fuller's Dome - Expo '67 Montreal Courtesy of B. Eggen (Univ. of Sussex) dispoptic 2013

18 The Nobel Prize in Chemistry 1996 was awarded jointly to Robert F
The Nobel Prize in Chemistry 1996 was awarded jointly to Robert F. Curl Jr., Sir Harold W. Kroto and Richard E. Smalley "for their discovery of fullerenes". @wiki A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are also called buckyballs, and they resemble the balls used in association football. Cylindrical ones are called carbon nanotubes or buckytubes. Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.[1] The first fullerene to be discovered, and the family's namesake, buckminsterfullerene (C60), was prepared in 1985 by Richard Smalley, Robert Curl, James Heath, Sean O'Brien, and Harold Kroto at Rice University. The name was an homage to Buckminster Fuller, whose geodesic domes it resembles. The structure was also identified some five years earlier by Sumio Iijima, from an electron microscope image, where it formed the core of a "bucky onion."[2] Fullerenes have since been found to occur in nature.[3] More recently, fullerenes have been detected in outer space.[4] According to astronomer Letizia Stanghellini, "It’s possible that buckyballs from outer space provided seeds for life on Earth.”[5] The discovery of fullerenes greatly expanded the number of known carbon allotropes, which until recently were limited to graphite, diamond, and amorphous carbon such as soot and charcoal. Buckyballs and buckytubes have been the subject of intense research, both for their unique chemistry and for their technological applications, especially in materials science, electronics, and nanotechnology. Quasecristal: possui estrutura, mas não tem simetria de translação translação dispoptic 2013

19 Outras estruturas dispoptic 2013

20 Exemplo de fulereto K3C60 Material com propriedades
supercondutoras (Tc = 20 K) C60 molecules are arranged in a face-centred cubic arrangement. If C60 is reduced with potassium metal it forms compounds such as K3C60, which is fcc C603- molecules with K+ ions in all octahedral and tetrahedral interstitial sites. K3C60 is an interesting material because of its superconducting properties (Tc = 20 K) and metal fullerides are the subject of much current research, for example in the group of the University of Liverpool's Prof Matthew Rosseinsky. dispoptic 2013

21 Raio atômico e raio iônico de alguns elementos em pm
Uma situação importante para todos os efeitos na formação de uma estrutura cristalina Raio atômico e raio iônico de alguns elementos em pm dispoptic 2013

22 Prêmio Nobel de Química 2011
Dan Shechtman The Nobel Prize in Chemistry 2011 was awarded to Dan Shechtman "for the discovery of quasicrystals". Modelo atômico de alumínio – paládio - manganês (Al-Pd-Mn) superfície quase-cristalina. @wiki Dan Shechtman (Hebrew: דן שכטמן) (born January 24, 1941 in Tel Aviv)[1] is the Philip Tobias Professor of Materials Science at the Technion – Israel Institute of Technology, an Associate of the US Department of Energy's Ames Laboratory, and Professor of Materials Science at Iowa State University. On April 8, 1982, while on sabbatical at the U.S. National Bureau of Standards in Washington, D.C., Shechtman discovered the icosahedral phase, which opened the new field of quasiperiodic crystals.[2] He was awarded the 2011 Nobel Prize in Chemistry for "the discovery of quasicrystals".[3] dispoptic 2013

23 Quasicrystal Research: A film by Alexander Tuschinski - http://www
LINK dispoptic 2013

24 Como identificar a posição dos átomos?
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25 Sistema cristalino imperfeito Sistema amorfo
Lei de Bragg Lei de Bragg nl = 2d senq Sistema cristalino Sistema cristalino imperfeito Sistema amorfo qi = qf = q nl = 2dsenq dispoptic 2013

26 Como identificar os planos de reflexão?
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27 Índices de Miller Especificação de um plano de átomos por um conjunto de números hkl Intersecção x1y1z1 com sistema de eixos coordenados xyz $ um número s tal que o produto de s vezes o recíproco das intersecções x1y1z1 dará o menor conjunto de números inteiros com a mesma proporção de 1/x1 1/y1 1/z1 Assim: h = s/x k = s/y1 l = s/z1 Muito útil para sistemas cúbicos dispoptic 2013

28 Como está relacionada a rede direta com os índices de Miller ?
Plano 3x + y =a y x d r Intersecção com os eixos: 1/3 e 1/1 Índices de Miller: 1 3 Plano (13) Direção normal ao plano: [31] Eq. do plano: dispoptic 2013

29 família singular planos {hkl} (hkl) direções <uvw> [uvw]
Notação para famílias de planos e direções família singular planos {hkl} (hkl) direções <uvw> [uvw] Ângulo q entre duas direções: Normal de um plano com índices (hkl) é [hkl] para sistema cúbico (não é geral) Distância d entre planos adjacentes com índices (hkl) é: dispoptic 2013

30 Distribuição de densidade eletrônica
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31 Distribuição de densidade eletrônica do NaCl
Na => 1s22s2p63s1 Cl => 1s22s2p63s2p5 dispoptic 2013

32 Outras ferramentas necessárias
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33 Rede recíproca Como descrever a morfologia de um cristal
Difração de Raios-X Estrutura eletrônica Definição de bandas dispoptic 2013

34 Rede recíproca dispoptic 2013

35 FCC – rede recíproca dispoptic 2013

36 Hexagonal – rede recíproca
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37 Como é a contribuição para a intensidade das linhas do difratograma?
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38 Fator de estrutura Espalhamento por um elétron
Espalhamento por um átomo Espalhamento por uma célula dispoptic 2013

39 Espalhamento por um elétron
O que estamos procurando? Intensidade do feixe espalhado por um elétron de carga e e massa m a uma distância r do elétron e um ângulo a entre a direção de espalhamento e a direção de aceleração do elétron J.J. Thomson [ref. Reitz & Milford, Melissinos] Como é a intensidade num ponto P? dispoptic 2013

40 Eq de Tomson para o espalhamento de um feixe de Raios-X por um elétron
Raios-X na direção Ox média Eq de Tomson para o espalhamento de um feixe de Raios-X por um elétron dispoptic 2013

41 Espalhamento por um átomo
Fator de estrutura atômico dispoptic 2013

42 Espalhamento por uma célula
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43 Exemplos: dispoptic 2013

44 dispoptic 2013

45 Elements of x-ray diffraction
B. D. Cullity Localização: IFSC-F /548.83^C967e^2 ed.^e.4 dispoptic 2013

46 E como é em materiais não cristalinos? Radiografias de alta definição
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47 WILLIAM CONRAD ROENTGEN – Raio-X
FIRST X-RAY ANNA BERTHA ROENTGEN'S HAND Art of Roentgen's X-ray apparatus for imaging hand dispoptic 2013

48 Novas técnicas de imagem de R-X. Physics Today Julho 2000
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49 Óptica de Raios-X dispoptic 2013