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Master's Dissertation
DOI
https://doi.org/10.11606/D.43.2011.tde-26042012-145354
Document
Author
Full name
Antonio Claudio Michejevs Padilha
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2011
Supervisor
Committee
Santos, Maria Cristina dos (President)
Carvalho, Ana Claudia Monteiro
Itri, Rosangela
Title in Portuguese
Aglomerados de pentaceno e nanotubos de carbono: um estudo MM/MQ (mecânica molecular/mecânica quântica)
Keywords in Portuguese
Dinâmica molecular
Distorção de Peierls
Mecânica molecular
Nanotubos de carbono
Pentaceno
Teoria do funcional da densidade
Abstract in Portuguese
Nanotubos de carbono e polímeros condutores são fortes candidatos à miniaturização dos componentes eletrônicos disponíveis atualmente. Estudos teóricos afirmaram que 1/3 dos nanotubos seriam metálicos, enquanto que os outros seriam semicondutores, mas alguns grupos reportaram medidas experimentais evidenciando um pequeno gap eletrônico em tubos considerados metálicos. Protótipos de transístores compostos de nanotubos e moléculas orgânicas conjugadas foram propostos e foi observado que o recobrimento dos tubos por moléculas de pentaceno tornava os dispositivos menos suscetíveis à deposição de impurezas, o que diminuía a histerese na curva característica i x V, ao mesmo tempo que a formação de cristais de pentaceno era favorecida. Neste trabalho estudamos a estrutura eletrônica dos nanotubos (5,5) e (9,0) través de DFT e observamos presença de um gap nesses sistemas, assim como uma deformação de suas estruturas de ligações químicas, evidenciando a distorção de Peierls. O efeito do termo de troca de Hartree-Fock introduzido no funcional B3LYP foi avaliado variando-se seu peso e observando as propriedades destes sistemas. Em uma segunda etapa, utilizamos mecânica molecular e dinâmica molecular clássica com o campo de forças CVFF 950 e observamos a formação de estruturas de pentaceno em volta dos tubos, evidenciando o favorecimento da formação de cristais do mesmo quando depositado sobre os nanotubos.
Title in English
Pentacene and carbon nantubes clusters: A MM/MQ (molecular mechanics/quantum mechanics) study
Keywords in English
Density functional theory
Molecular dynamics
Molecular mechanics
Pentacene and carbon nantubes
Peoerls distortion
Abstract in English
Carbon Nanotubes and conducting polymers are strong candidates for use in nanoscale electronic devices. Theoretical studies claimed that 1/3 of the nanotubes are metallic, while the others are semiconductors, but some groups have reported experimental measurements of a small electronic gap in tubes considered metallic. Prototype transistors made of nanotubes and organic conjugated molecules were proposed and it has been noticed that the coverage of the tubes by pentacene molecules made those trasistors less susceptible to impurity deposition, reducing the hysteresis in the characteristic I x V curve, while the formation of pentacene cristals was favored. In this work, we studied the electronic structure of the nanotubes (5,5) and (9,0) using DFT and noticed an electronic gap in those systems, as well as a deformation of their structures, similar to a Peierls distortion. The effect of the Hartree-Fock exchange included in the B3LYP functional was studied, as we varied its weight to obtain some properties of those systems. Later, we used molecular mechanics and classical molecular dynamics with the CVFF 950 force field and obtained structures compatible with pentacene crystals around the tubes, showing that the tubes in fact favor the formation of of these structures around them.
 
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Publishing Date
2012-05-21
 
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