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Search Results: 1 - 10 of 328940 matches for " V. R. Coluci "
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Prediction of Giant Electro-actuation for Carbon Nanoscrolls
R. Rurali,V. R. Coluci,D. S. Galv?o
Physics , 2006,
Abstract: We study by first-principles calculations the electro-mechanical response of carbon nanoscrolls. We show that although they present a very similar behavior to carbon nanotubes for what concerns the axial deformation sensitivity, they exhibit a radial response upon charge injection which is up to one order of magnitude larger. In association with their high stability, this behavior make them a natural choice for a new class of very efficient nano-actuators.
Thermophoretically Driven Carbon Nanotube Oscillators
V. R. Coluci,V. S. Timóteo,D. S. Galv?o
Physics , 2010, DOI: 10.1063/1.3276546
Abstract: The behavior of a nanodevice based upon double-walled carbon nanotube oscillators driven by periodically applied thermal gradients (7 and 17 K/nm) is investigated by numerical calculations and classical molecular dynamics simulations. Our results indicate that thermophoresis can be effective to initiate the oscillator and that suitable heat pulses may provide an appropriate way to tune its behavior. Sustained regular oscillatory as well as chaotic motions were observed for the systems investigated in this work.
New Families of Carbon Nanotubes
V R. Coluci,S F Braga,S B Legoas,D S Galvao,R H Baughman
Physics , 2002,
Abstract: Fundamentally new families of carbon single walled nanotubes are proposed. These nanotubes, called graphynes, result from the elongation of covalent interconnections of graphite-based nanotubes by the introduction of yne groups. Similarly to ordinary nanotubes, arm-chair, zig-zag, and chiral graphyne nanotubes are possible. Electronic properties, predicted using tight-binding and ab initio density functional methods, show a rich variety of metallic and semiconducting behaviors.
Doping of zigzag carbon nanotubes through the encapsulation of small fullerenes
K. S. Troche,V. R. Coluci,R. Rurali,D. S. Galv?o
Physics , 2006,
Abstract: In this work we investigated the encapsulation of C$_20$ and C$_30$ fullerenes into semiconducting carbon nanotubes to study the possibility of bandgap engineering in such systems. Classical molecular dynamics simulations coupled to tight-binding calculations were used to determine the conformational and electronic properties of carbon nanotube supercells containing up to 12 fullerenes. We have observed that C$_20$ fullerenes behave similarly to a p-type dopant while C$_30$ ones work as n-type ones. For larger diameter nanotubes, where fullerene patterns start to differ from the linear arrangements (peapods), the doping features are preserved for both fullerenes, but local disorder plays an important role and significantly alters the electronic structure. The combined incorporation of both fullerene types (hybrid encapsulation) into the same nanotube leads to a behavior similar to that found in electronic junctions in Silicon-based electronic devices. These aspects can be exploited in the design of nanoelectronic devices using semiconducting carbon nanotubes.
Designing Conducting Polymers Using Bioinspired Ant Algorithms
Bruno V. C. Martins,Gustavo Brunetto,Fernando Sato,Vitor R. Coluci,Douglas S. Galvao
Physics , 2007, DOI: 10.1016/j.cplett.2008.01.037
Abstract: Ant algorithms are inspired in real ants and the main idea is to create virtual ants that travel into the space of possible solution depositing virtual pheromone proportional to how good a specific solution is. This creates a autocatalytic (positive feedback) process that can be used to generate automatic solutions to very difficult problems. In the present work we show that these algorithms can be used coupled to tight-binding hamiltonians to design conducting polymers with pre-specified properties. The methodology is completely general and can be used for a large number of optimization problems in materials science.
Molecular Dynamics Simulations of Carbon Nanotubes as Gigahertz Oscillators
S. B. Legoas,V. R. Coluci,S. F. Braga,P. Z. Coura,S. O. Dantas,D. S. Galvao
Physics , 2002, DOI: 10.1103/PhysRevLett.90.055504
Abstract: Recently Zheng and Jiang [PRL 88, 045503 (2002)], based on static models, have proposed that multiwalled carbon nanotubes could be the basis for a new generation of nanooscilators in the several gigahertz range. In this work we present the first molecular dynamics simulation for these systems. Different nanotube types were considered in order to verify the reliability of such devices as gigahertz oscillators. Our results show that these nanooscillators are dynamically stables when the radii difference values between inner and outer tubes are of ~ 3.4 A. Frequencies as large as 38 GHz were observed, and the calculated force values are in good agreement with recent experimental investigations. Moreover, our results contradict some predictions made by Zheng and Jiang.
Atomistic Study of the Encapsulation of Diamondoids Inside Carbon Nanotubes
Karla S. Troche,Vitor R. Coluci,Douglas S. Galvao
Physics , 2007,
Abstract: The encapsulation of hydrogen-terminated nanosized diamond fragments (the so-called diamondoids) into armchair single walled carbon nanotubes with diameters in the range of 1.0 up to 2.2 nm has been investigated using classical molecular dynamics simulations. Diameter dependent molecular ordered phases were found for the encapsulation of adamantane (C10H16), diamantane (C14H20), and dihydroxy diamantane (C14H20O2). The same types of chiral ordered phases (double, triple, 4- and 5-stranded helices) observed for the encapsulation of C60 molecules were also observed for diamondoids. On the other hand, some achiral phases comprising layered structures were not observed. Our results also indicate that the modification of diamantane through functionalization with hydroxyl groups can lead to an enhancement of the packing of molecules inside the nanotubes compared to nonfunctionalized compounds. Comparisons to hard-sphere models are also presented revealing differences, specially when more asymmetrical diamondoids are considered. For larger structures (adamantane tetramers) we have not observed long-range ordering for nanotubes with diameters in the range of 1.49 to 2.17 nm but only a tendency to form incomplete helical structures.
Atomistic Simulations of the Mechanical Properties of 'Super' Carbon Nanotubes
Vitor R. Coluci,Nicola M. Pugno,Socrates O. Dantas,Douglas S. Galvao,Ado Jorio
Physics , 2007, DOI: 10.1088/0957-4484/18/33/335702
Abstract: The mechanical properties of the so-called `super' carbon nanotubes (STs) are investigated using classical molecular dynamics simulations. The STs are built from single walled carbon nanotubes (SWCNTs) connected by Y-like junctions forming an ordered carbon nanotube network that is then rolled into a seamless cylinder. We observed that the ST behavior under tensile tests is similar to the one presented by fishing nets. This interesting behavior provides a way to vary the accessible channels to the inner parts of STs by applying external mechanical load. The Young's modulus is dependent on the ST chirality and it inversely varies with the ST radius. Smaller reduction of breaking strain values due to temperature increase is predicted for zigzag STs compared to SWCNTs. The results show that, for STs with radius ~ 5 nm, the junctions between the constituent SWCNTs play an important role on the fracture process. The Young's modulus and tensile strength were estimated for hierarchical higher-order STs using scaling laws related to the ST fractal dimension. The obtained mechanical properties suggest that STs may be used in the development of new porous, flexible, and high-strength materials.
Entanglement and the nonlinear elastic behavior of forests of coiled carbon nanotubes
Vitor R. Coluci,Alexandre F. Fonseca,Douglas S. Galvao,Chiara Daraio
Physics , 2007, DOI: 10.1103/PhysRevLett.100.086807
Abstract: Helical or coiled nanostructures have been object of intense experimental and theoretical studies due to their special electronic and mechanical properties. Recently, it was experimentally reported that the dynamical response of foamlike forest of coiled carbon nanotubes under mechanical impact exhibits a nonlinear, non-Hertzian behavior, with no trace of plastic deformation. The physical origin of this unusual behavior is not yet fully understood. In this work, based on analytical models, we show that the entanglement among neighboring coils in the superior part of the forest surface must be taken into account for a full description of the strongly nonlinear behavior of the impact response of a drop-ball onto a forest of coiled carbon nanotubes.
Rotational dynamics and polymerization of C$_{60}$ in C$_{60}$-cubane crystals: A molecular dynamics study
Vitor R. Coluci,Fernando Sato,Scheila F. Braga,Munir S. Skaf,Douglas S. Galvao
Physics , 2009, DOI: 10.1063/1.2965885
Abstract: We report classical and tight-binding molecular dynamics simulations of the C$_{60}$ fullerene and cubane molecular crystal in order to investigate intermolecular dynamics and polymerization processes. Our results show that, for 200 K and 400 K, cubane molecules remain basically fixed, presenting only thermal vibrations, while C$_{60}$ fullerenes show rotational motions. Fullerenes perform "free" rotational motions at short times ($\lesssim$ 1 ps), small amplitude hindered rotational motions (librations) at intermediate times, and rotational diffusive dynamics at long times ($\gtrsim$ 10 ps). The mechanisms underlying these dynamics are presented. Random copolymerization among cubanes and fullerenes were observed when temperature is increased, leading to the formation of a disordered structure. Changes in the radial distribution function and electronic density of states indicate the coexistence of amorphous and crystalline phases. The different conformational phases that cubanes and fullerenes undergo during the copolymerization process are discussed.
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