Author: Renato Pinto Reveggino

Controlling dissociative adsorption for effective growth of carbon nanotubes

Renato Pinto Reveggino

Diss-adsopt-APL2004

Dissociative adsorption has been widely simplified as part of the vapor–liquid–solid (VLS) growth

model. We found that the addition of specific carrier gases can critically modify the growth rate and

growth density of multiwall carbon nanotubes (MWNTs). These results were explained by

dissociative adsorption of C2H2 molecules and a solid-core VLS growth model. Based on these

integrated mechanisms, vertically aligned MWNTs were grown with an initial growth rate as high

as ,800 mm/h. This efficient growth process results at temperature and C2H2 partial pressures at

which the decomposition and segregation rates of carbon are balanced. Appropriate use of carrier

gas is one of the factors that could facilitate efficient and continuous growth of carbon nanotubes in

the future.

Surfactant-free dielectrophoretic deposition of multi-walled carbon nanotubes with tunable deposition density

Renato Pinto Reveggino

DEP-Carbon2010

The effects of AC field strength and AC frequency on the density of dielectrophoretically deposited multi-walled carbon nanotubes (MWCNTs) were investigated and explained in terms of existing theory. We show that while both parameters can be used to control deposition density, the experimentally observed frequency trend can not be explained by the theoretical Clausius–Mossotti factors. We demonstrate the ability to make surfactant-free dispersions of long, difficult to disperse MWCNTs and use them with dielectrophoresis to make clean, single and few connections between electrodes.

Dielectrophoretic Deposition of Carbon Nanotubes with Controllable Density and Alignment

Renato Pinto Reveggino

DEP_CNT_MRS2008

Controlled deposition of carbon nanotubes (CNTs) across desired electrodes is important

for the fabrication of nanoelectronic devices. Dieletrophoresis (DEP) has been recognized as a

convenient and affordable technique for the deposition of nanotubes and nanowires on

electrodes. Although DEP has been quite well studied for dielectric particles, the application for

depositing nanotubes is still at the early stage of development. Here, we show that multi-walled

CNTs can be deposited by DEP with controllable density and degree of alignment.

Functionalization, Dispersion, and Cutting of Boron Nitride Nanotubes in Water

Renato Pinto Reveggino

CuttingBNNTs-JPC-C-2012

High-quality boron nitride nanotubes (BNNTs) were functionalized for the first time with water-soluble and biocompatible PEGylated phospholipid [methoxy-poly(ethylene glycol)-1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N conjugates (mPEG-DSPE)]. We found that BNNTs can be suspended in water for more than 3 months without precipitation. By comparing the dispersion stability of mPEG-DSPE/BNNTs in various solvents and the related Hansen solubility parameters, we found that polarized and hydrogen bonds between water and the hydrophilic mPEG play important roles in maintaining stable dispersion of BNNTs and preventing aggregation of mPEG-DSPE/BNNTs in the solutions. This has led to the formation of composite films with well-dispersed BNNTs and the coating of self-assembled monolayer (SAM) BNNTs. Furthermore, the lengths of these functionalized BNNTs can be shorterned, for the first time, from >10 μm to ∼500 nm by ultrasonication. Experiments suggest that effective dispersion of BNNT in solution is necessary for such cutting, where effective energy transfer from the sonicator to nanotubes is achieved. Our results will form the basis for stable functionalization, dispersion, and effective cutting of BNNTs with water-soluble and biocompatible PEGylated phospholipid, which are important for biomedical and composite applications.

Growth of adhesive cubic phase boron nitride films without argon ion bombardment

Renato Pinto Reveggino

Cubic-BN-DMR2006

Previously, in situ bombardment of massive ions (Ar+, Kr+, etc.) was considered to be necessary for the formation of c-BN films. Because of

the accumulated stress, bombardment of massive ions has led to the formation of c-BN films with poor adhesion. Here we show that c-BN films

can be grown without involving bombardment of massive ions. This is achieved by using plasma-assisted pulsed-laser deposition (PLD) in pure

N2 RF plasma. Furthermore, we show that c-BN films can be grown in a vacuum ( ̈105 mbar during growth) by PLD without auxiliary ion

source. We show that these are possible at a reduced deposition rate. Energetic growth species initiated by PLD and the pure N2 plasma is

sufficient to form adhesive c-BN films at moderate deposition rate as long as the energy transfer rate per growth species is sufficient.

D 2005 Elsevier B.V. All rights reserved.

Vertically Aligned Carbon Nanotubes as the Sputter Resist in Space Propulsive Systems

Renato Pinto Reveggino

CNTSpacePropulsionMRS2005

Two-types of vertically aligned multi-walled carbon nanotubes (VA-MWNTs) are

evaluated as the protective coatings against ion erosion in electric propulsion systems. A

series of experiments have been conducted to understand the erosion rate and erosion

mechanism of these VA-MWNTs. These experiments were carried out with Xe

propellant at an ion current density of 5 mA/cm2. We found that the erosion rates of both

types of VA-MWNTs were changing with time. Such a nonlinear erosion process is

explained according to a possible erosion mechanism.

High-density vertically aligned multiwalled carbon nanotubes with tubular structures

Renato Pinto Reveggino

CNTs-APL2005

Ammonia sNH3d gas was thought to be essential for the growth of vertically aligned multiwalled

carbon nanotubes sVA-MWCNTsd and led to the formation of bamboo-like structures. Here, we

show that VA-MWCNTs with ideal tubular structures can be grown on substrates by various mixed

gases with or without NH3 gas. The growth of these VA-MWCNTs is guided by a growth model that

combined the dissociative adsorption of acetylene molecules sC2H2d and the successive

vapor-liquid-solid growth mechanism. Results indicate that the key factor for growing these

VA-MWCNTs is a balance between the decomposition rate of the C2H2 molecules on the iron

catalyst and the subsequent diffusion and segregation rates of carbon.

© 2005 American Institute of Physics. fDOI: 10.1063/1.1952575g

Effect of Carrier Gas on the Growth Rate, Growth Density, and Structure of Carbon Nanotubes

Renato Pinto Reveggino

CNT_Syn_MRS2004

We attempt to understand the fundamental factors that determine the growth rate

of carbon nanotubes. In a series of experiments on growing multiwall carbon nanotubes

(MWNTs) by thermal chemical vapor deposition, we found that the addition of carrier

gas and the type of carrier gas can change the growth rate, growth density, and structures

of MWNTs. We explain these results based on the dissociative adsorption of C2H2 on Fe

nanoparticles and the vapor-liquid-solid (VLS) growth model. Finally, high-density,

vertically aligned MWNTs were grown when decomposition and segregation rates of

carbon were balanced.

Testing Multiwall Carbon Nanotubes on Ion Erosion for Advanced Space Propulsion

Renato Pinto Reveggino

CNT_SpacePropulsionMRS2004

Are carbon nanotubes more resistant than diamonds against ion erosion?

Here, we report an evaluation of multiwall carbon nanotubes (MWNTs) as the protective

coating against plasma erosion in advanced space propulsion systems. We have compared

polycrystalline diamond films with MWNTs, amorphous carbon (a-C) and boron nitride

(BN) films. Two types of MWNTs were investigated including vertically aligned (VA)

MWNTs, and those horizontally laid on the substrate surfaces. Only diamond films and

VA-MWNTs survived erosion by 250 eV krypton ions of a flight-quality Hall-effect

thruster. VA-MWNTs are found to bundle at their tips after ion erosion.

A Dual-RF-Plasma Approach for Controlling the Graphitic Order and Diameters of Vertically-Alligned Multiwall Carbon Nanotubes

Renato Pinto Reveggino

CNT_MRS2005

Plasma enhanced chemical vapor deposition (PECVD) is a unique technique for growing

vertically-aligned multiwall carbon nanotubes (VA-MWNTs) at controllable tube densities. This

technique is of considerable importance for low temperature growth of VA-MWNTs at desired

locations. However, the graphitic order of these MWNTs is inferior to those grown by laser

ablation, arc discharge, and thermal CVD techniques. Previously, these VA-MWNTs were

grown by a one-plasma approach (DC, microwave etc), either for gas decomposition or substrate

biasing. Here, we describe a dual-RF plasma enhanced CVD (dual-RF-PECVD) technique that

offers unique capability for controlling the graphitic order and diameters of VA-MWNTs.