On the existence of ordered phases of encapsulated diamondoids into carbon nanotubes

We have investigated some diamondoids encapsulation into single walled carbon nanotubes (with diameters ranging from1.0 up to 2.2 nm) using fully atomistic molecular dynamics simulations. Diamondoids are the smallest hydrogen-terminated nanosized diamond-like molecules. Diamondois have been investigated for a large class of applications, ranging from oil industry to pharmaceuticals. Molecular ordered phases were observed for the encapsulation of adamantane, diamantane, and dihydroxy diamantanes. Chiral ordered phases, such as; double, triple, 4- and 5-stranded helices were also observed for those diamondoids. Our results also indicate that the modification of diamondoids through chemical functionalization with hydroxyl groups can lead to an enhancement of the molecular packing inside the carbon nanotubes in comparison to non-functionalized molecules. For larger diamondoids (such as, adamantane tetramers), we have not observed long-range ordering, but only a tendency of incomplete helical structural formation. © 2012 Materials Research Society.

When small is different: The case of membranes inside tubes

Recently, classical elasticity theory for thin sheets was used to demonstrate the existence of a universal structural behavior describing the confinement of sheets inside cylindrical tubes. However, this kind of formalism was derived to describe macroscopic systems. A natural question is whether this behavior still holds at nanoscale. In this work, we have investigated through molecular dynamics simulations the structural behavior of graphene and boron nitride single layers confined into nanotubes. Our results show that the class of universality observed at macroscale is no longer observed at nanoscale. The origin of this discrepancy is addressed in terms of the relative importance of forces and energies at macro and nano scales. © 2012 Materials Research Society.

On the unzipping mechanisms of carbon nanotubes: Insights from reactive molecular dynamics simulations

Unzipping carbon nanotubes (CNTs) is considered one of the most promising approaches for the controlled and large-scale production of graphene nanoribbons (GNR). These structures are considered of great importance for the development of nanoelectronics because of its dimensions and intrinsic nonzero band gap value. Despite many years of investigations some details on the dynamics of the CNT fracture/unzipping processes remain unclear. In this work we have investigated some of these process through molecular dynamics simulations using reactive force fields (ReaxFF), as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. We considered multi-walled CNTs of different dimensions and chiralities and under induced mechanical stretching. Our preliminary results show that the unzipping mechanisms are highly dependent on CNT chirality. Well-defined and distinct fracture patterns were observed for the different chiralities. Armchair CNTs favor the creation of GNRs with well-defined armchair edges, while zigzag and chiral ones produce GNRs with less defined and defective edges. © 2012 Materials Research Society.

Controlled route to the fabrication of carbon and boron nitride nanoscrolls: A molecular dynamics investigation

Carbon nanoscrolls (graphene layers rolled up into papyrus-like tubular structures) are nanostructures with unique and interesting characteristics that could be exploited to build several new nanodevices. However, an efficient and controlled synthesis of these structures was not achieved yet, making its large scale production a challenge to materials scientists. Also, the formation process and detailed mechanisms that occur during its synthesis are not completely known. In this work, using fully atomistic molecular dynamics simulations, we discuss a possible route to nanoscrolls made from graphene layers deposited over silicon oxide substrates containing chambers/pits. The scrolling mechanism is triggered by carbon nanotubes deposited on the layers. The process is completely general and can be used to produce scrolls from other lamellar materials, like boron nitride, for instance. © 2013 American Institute of Physics.

Photodetection with gate-controlled lateral BJTs from standard CMOS technology

The silicon-based gate-controlled lateral bipolar junction transistor (BJT) is a controllable four-terminal photodetector with very high responsivity at low-light intensities. It is a hybrid device composed of a MOSFET, a lateral BJT, and a vertical BJT. Using sufficient gate bias to operate the MOS transistor in inversion mode, the photodetector allows for increasing the photocurrent gain by 106 at low light intensities when the base-emitter voltage is smaller than 0.4 V, and BJT is off. Two operation modes, with constant voltage bias between gate and emitter/source terminals and between gate and base/body terminals, allow for tuning the photoresponse from sublinear to slightly above linear, satisfying the application requirements for wide dynamic range, high-contrast, or linear imaging. MOSFETs from a standard 0.18-μm triple-well complementary-metal oxide semiconductor technology with a width to length ratio of 8 μm /2 μm and a total area of ∼ 500μm2 are used. When using this area, the responsivities are 16-20 kA/W. © 2001-2012 IEEE.

Social and environmental indexes to determine the impacts of closed neighbourhoods in Brazil

São Paulo State, in Brazil, is getting increasingly crowded, like in other third world countries around the world, so should give great importance to city development. This work considered the phenomenon of closed neighbourhoods (CN) as an important factor to city planning, papers report many impacts of this model of neighbourhoods in other countries, but in Brazil its impacts are not yet well listed in the literature. The aim of this work was to determine indicators to achieve the social and environmental performances and verify their applicability on three different closed neighbourhoods in São Paulo state, Brazil. The indicators were condensed on indexes: water management, waste management, energy and emissions, legal compliance, environment and buildings, risk management, health and education and governance. The preliminary results indicated several social and environmental problems in all indexes. © 2013 WIT Press.

Modernidade, medo e violência: reflexões teóricas e o caso de Marília/SP

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação do método de sucção de encéfalo de morcegos (Chiroptera, Mammalia) para diagnóstico da raiva

Pós-graduação em Ciência Animal - FMVA

Acesso restrito: reflexões sobre a qualidade ambiental percebida por habitantes de condomínios horizontais

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Condomínios residenciais: segregação, auto-segregação imposta no município de Rio Claro (SP)

Pós-graduação em Geografia - IGCE

Férmions em campos externos em 1+1 e 2+1 dimensões

Pós-graduação em Física - FEG

Novas centralidades e novos habitats: caminhos para a fragmentação urbana em Marília (SP)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cálculos de estrutura eletrônica de materiais mediante combinação linear de orbitais atômicos

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Metodologia para avaliação de desempenho ambiental em condomínios fechados

Pós-graduação em Geociências e Meio Ambiente - IGCE

Fatores homólogos aos fatores de crescimento fibroblásticos são expressos em folículos antrais e corpos lúteos bovinos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)