Nucleation and growth of carbon nanotubes in catalytic chemical vapor deposition

The process of nucleation of multiwall carbon nanotubes in chemical vapor deposition process with nickel as catalyst and methane as a carbon precursor is analyzed. The nucleation is considered as a specific instability developed on the surface of a metal catalyst particle supersaturated with carbon. The energy released in graphitization of carbon from the metal-carbon solution is shown to be crucial for the nanotube nucleation. The energy released may be high enough for substantial metal heating resulting in partial liquefaction of the catalyst particle. The proposed mechanism can be called vapor-solid-liquid-solid (VSLS) as the catalyst particle may be in a mixed solid-liquid (or liquidlike) state during nucleation and unstable phases of nanotube growth. (c) 2007 American Institute of Physics.102

Low contact resistivity and strain in suspended multilayer graphene

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Method to prepare suspended multilayer graphene (MLG) flakes and to form highly conductive (contact resistivity of similar to 0.1 k Omega mu m(2)) and tight mechanical connection between MLG and metal electrodes is described. MLG flakes prepared from natural graphite were precisely deposited over tungsten electrodes using dielectrophoresis, followed by high-temperature thermal annealing in high-vacuum. Considerable strain induced in the suspended part of flakes was revealed by Raman imaging. (C) 2010 American Institute of Physics. [doi:10.1063/1.3528354]9725Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)INCT NAMITECFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Mode transitions and hysteresis in inductively coupled plasmas

Optical emission spectroscopy as a noninvasive plasma diagnostic was employed to study mode transitions and hysteresis in an inductively coupled plasma in Ar and Ar/N-2 mixtures. Using selected Ar lines, basic plasma parameters, relevant to the analysis of the mode transitions, were evaluated. Small changes of the electron energy distribution function in the vicinity of the mode transition were detected. The role of metastable Ar atoms in mode transitions and in a hysteresis was clarified. Enhanced production of metastables in the hysteresis region as well as faster transitions in plasmas with higher influence of metastables were observed. (c) 2007 American Institute of Physics.101

Deposition of sacrificial silicon oxide layers by electron cyclotron resonance plasma

Electron cyclotron resonance plasmas with SiH4/O-2/Ar mixtures were used for deposition of thin films of silicon oxide, to be employed as sacrificial layers in microelectromechanical system (MEMS) fabrication. The grown films were characterized by Fourier transform infrared and ellipsometry. Optical emission spectroscopy and Langmuir probe were used for plasma characterization. It has been shown that OH molecules generated in the plasma play an important role in formation of films suitable as sacrificial layers for MEMS fabrication. Extremely high etch rates of grown oxide films (up to 10 mu m/min) were obtained, allowing fabrication of high quality poly-Si suspended structures. (c) 2007 American Vacuum Society.2541166117

Synthesis of carbon nanotubes directly over TEM grids aiming the study of nucleation and growth mechanisms

A novel approach to produce electron-transparent multi-layer membranes over TEM grids for transmission electron microscopy analysis is presented. The membranes have been used to grow and analyze carbon nanostructured materials in a thermal-chemical vapor deposition process using Ni and Cu as catalysts and silicon oxide thin films as support layers, at temperatures as high as 900 degrees C. It is important that conditions of the synthesis using the electron-transparent multi-layer membrane system are similar to those for a conventional chemical vapor deposition process, where oxidized silicon wafers are employed. In particular, the thickness of the silicon oxide and the catalyst layers are the same, and similar carbon tubular structures were grown using both substrates. The use of membranes was crucial especially for the study of the nucleation mechanism for carbon nanotubes. These electron-transparent multi-layer membranes are relatively easy to obtain and they can be used for transmission electron microscopy studies of high-temperature synthesis of different nanostructured materials. (C) 2008 Elsevier B.V. All rights reserved.254133890389

Comparative analysis of thin Ni and CoNiMnP magnetic films

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The results of an investigation of thin Ni and CoNiMnP films deposited by electroplating over polyurethane-acrylate flexible substrates are presented. To improve magnetic properties of the films, an electroplating process was carried out with assistance of a strong magnetic field (3900 G). The evaluated film properties were coercivity, remanence, maximum energy product, adherence and film composition. Comparison between the magnetic properties of the samples has shown that Ni and CoNiMnP films are suitable for distinct areas of applications in micro-devices: vibrating diaphragms and micro-magnet machines, respectively. (c) 2012 Elsevier B.V. All rights reserved.5201548714874Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)INCT NAMITECFundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Silicon nitride thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition for micromechanical system applications

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Thin silicon nitride films have been deposited by a low temperature (20 degrees C) Electron Cyclotron Resonance (ECR) plasma directly on Si substrates. Varying the process pressure, gas composition and radio frequency bias power, films with different properties were obtained. Characterization by Fourier transform infra-red spectrometry reveals the presence of Si-N, Si-H and N-H bonds in the films. Refractive indexes in the range from 1.77 to 2.9 and deposition rates from 13 to 18 nm/min were determined by ellipsometry. Buffered hydrofluoric acid (BHF) etch rates from 0.7 to 509 nm/min, and KOH etch rates lower than I nm/min were obtained. Optical emission spectroscopy showed a strong correlation between the concentration of NH molecules produced in the plasma and porosity of the films. Finally, the films that presented high resistance to etching in KOH and BHF were used to fabricate suspended membranes on Si substrates. With these results, the ECR plasma produced SiNx films that have been used for fabrication of membranes in microelectromechanical systems. (c) 2008 Elsevier B. V. All rights reserved.5162177777782Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FINEPConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Nonlocal laser annealing to improve thermal contacts between multi-layer graphene and metals

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)The accuracy of thermal conductivity measurements by the micro-Raman technique for suspended multi-layer graphene flakes has been shown to depend critically on the quality of the thermal contacts between the flakes and the metal electrodes used as the heat sink. The quality of the contacts can be improved by nonlocal laser annealing at increased power. The improvement of the thermal contacts to initially rough metal electrodes is attributed to local melting of the metal surface under laser heating, and increased area of real metal-graphene contact. Improvement of the thermal contacts between multi-layer graphene and a silicon oxide surface was also observed, with more efficient heat transfer from graphene as compared with the graphene-metal case.2415Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)INCT NAMITECMinistry of Education and Science of the Russian Federation [11.519.11.3020, 11.519.11.3026]Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Ministry of Education and Science of the Russian Federation [11.519.11.3020, 11.519.11.3026

Size-controlled synthesis of graphite nanoflakes and multi-layer graphene by liquid phase exfoliation of natural graphite

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Multi-layer graphene and graphite nanofiakes were produced through graphite liquid exfoliation using organic solvents. The nanoflakes size distribution was statistically analyzed, with the number of measured samples being high enough (from similar to 200 to 900) for reliable evaluation of the statistical model. The nanofiakes size data were found to follow a log-normal distribution, with higher fraction of large size flakes as compared to a conventional normal distribution. The same kind of distribution was also obtained for nanofiakes thickness. Based on these findings, the detailed mechanism of the pristine polycrystalline graphite exfoliation in a liquid phase due to formation and collapse of cavitation bubbles was discussed. The high quality of nanoflakes was confirmed by Raman spectroscopy. (C) 2013 Elsevier Ltd. All rights reserved.69525535Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)INCT NAMITEC, (Brazil)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Fabrication of high-aspect ratio silicon nanopillars and nanocones using deep reactive ion etching

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Bosch type processes have been employed to fabricate nanostructured Si surfaces. Nanopillars and nanocones in Si have been fabricated using different techniques for Ni micromasking. Plasma redeposition of Ni was found to be responsible for Si pillar formation with diameters varying in the submicron range. A possibility to produce tilted nanopillars with tilt angles up to as high as 25 degrees has been demonstrated. In other method, previously deposited and annealed thin Ni films were employed. Smaller Ni nanoislands were obtained, and the formation of Si nanocones was demonstrated using longer passivation steps. In this case, reflection coefficients as low as 1.2% were obtained for the optimized etching process time.27627322736Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)NAMITECConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP