Author: Renato Pinto Reveggino

Structural control of vertically aligned multiwalled carbon nanotubes by radio-frequency plasmas

Renato Pinto Reveggino

PECVD_CNTs_APL2005

Carbon nanotubes CNTs are among the important materials for the advancement of future nanoscience and nano-technology. Recently, vertically aligned multiwalled carbon nanotubes VA-MWCNTs have gained additional attention for innovative applications, such as nanotubes antennas,1vertical transistors,2,3 and vertical biosensors.4 Ideally, these applications require VA-MWCNTs to be grown at desired patterns. Plasma-enhanced chemical vapor deposition PECVD is the only technique for growing individual VA-MWCNTs at desired locations. However, the graphitic order of these VA-MWCNTs is inferior to the multiwall CNTs grown by arc discharge5 and thermal chemical vapordeposition.6–8 This has been a long-standing issue for realis-tic uses of VA-MWCNTs in applications, such as electron field emission devices.9–13

 

Nanotubes and Related Nanostructures–2014

Renato Pinto Reveggino

opl1700fm

Carbon nanotubes and related nanostructures, including nanosheets have attracted tremendous attention for their unique structures and intriguing properties. These nanomaterials have been widely investigated—from theory, synthesis, and characterization to applications in electronic devices, energy generation and storage, biological and chemical sensors, etc. In addition, non-carbon nanostructures such as nanotubes and nanosheets of boron nitride (BN) have gained increasing interest. To facilitate scientific interaction among students and researchers on the latest advancements in this area, Symposium MM – Nanotubes and Related Nanostructures, was organized and held on Apr. 21–25 at the 2014 MRS Spring Meeting in San Francisco, California. The symposium organizers were Don Futaba (National Institute of Advanced Industrial Science and Technology), Annick Loiseau (Laboratoire d’Etude des Microstructures), Yoke Khin Yap (Michigan Technological University), and Ming Zheng (National Institute of Standards and Technology). This proceedings volume consists of peer-reviewed papers presented in the symposium, including invited and contributed presentations. These papers represent a snapshot of topics discussed in both theoretical and experimental aspects. We hope this publication will contribute toward productive research in the area of nanotubes and related nanostructures.

Boron nitride nanotubes grown just like carbon nanotubes

Renato Pinto Reveggino

NanoTodayBNNTs

Boron nitride nanotubes (BNNTs) have extraordinary mechanical properties ideal as reinforcements in composites and offer the possibility of a tunable band gap for electronic applications. But synthesizing BNNTs has proven difficult, with current methods requiring high temperatures, special-ized instrumentation and producing nanotubes of low quality contaminated with impurities. Now researchers from Michigan Technological University believe they have changed all this using an approach that makes the growth of BNNTs as simple and convenient as carbon nanotubes [C.H. Lee et al., Chem. Mater. (2009), doi:10.1021/cm903287u]. Using catalytic chemical vapordeposition (CCVD) at 1200 ◦C with MgO, Ni or Fe catalysts, Yoke Khin Yap and his team have achieved patterned growth of BNNTs directly on Si substrates for the first time

A Simple and Universal Technique To Extract One- and Two- Dimensional Nanomaterials from Contaminated Water

Renato Pinto Reveggino

NanoExtractionACS2015

We demonstrate a universal approach to extract one- and two-dimensional nanomaterials from contaminated water, which is based on a microscopic oil−water interface trapping mechanism. Results indicate that carbon nanotubes, graphene, boron nitride nanotubes, boron nitride nanosheets, and zinc oxide nanowires can be successfully extracted from contaminated water at a successful rate of nearly 100%. The effects of surfactants, particle shape, and type of organic extraction fluids are evaluated. The proposed extraction mechanism is also supported by in situ monitoring of the extraction process. We believe that this extraction approach will prove important for the purification of water contaminated by nanoparticles and will support the widespread adoption of nanomaterial applications.

MoS2 Quantum Dot: Effects of Passivation, Additional Layer, and h‐BN Substrate on Its Stability and Electronic Properties

Renato Pinto Reveggino

MoS2-JPCC2015

The inherent problem of a zero-band gap in graphene has provided motivation to search for the next-generation electronic materials including transition metal dichalcogenides, such as MoS2. In this study, a triangular MoS2 quantum dot (QD) is investigated to see the effects of passivation, additional layer, and the h-BN substrate on its geometry, energetics, and electronic properties. The results of density functional theory calculations show that the monolayer QD is metallic in nature, mainly due to the coordinatively unsaturated Mo atoms at the edges. This is reaffirmed by the passivation of the S edge atoms, which does not significantly modify its metallic character. Analysis of the chemical topology finds that the Mo−S bonds associated with the edge atoms are predominantly covalent despite the presence of metallic states. A bilayer QD is more stable than its monolayer counterpart, mainly due to stabilization of the dangling bonds of the edge atoms. The degree of the metallic character is also considerably reduced as demonstrated by the I−V characteristics of a bilayer QD. The binding strength of a monolayer QD to the h-BN substrate is predicted to be weak. The substrate-induced modifications in the electronic structure of the quantum dot are therefore not discernible. We find that the metallic character of the QD deposited on the insulating substrate can therefore be exploited to extend the functionality of MoS2-based nanostructures in catalysis and electronics applications at the nanoscale level.

A simple scheme of molecular electronic devices with multiwalled carbon nanotubes as the top electrodes

Renato Pinto Reveggino

Molectronics-Carbon-2012

A simple fabrication scheme for molecular electronic junctions is presented with multi-walled carbon nanotubes (MWCNTs) as the top electrodes. Results indicate that our approach retains the molecular character of the chosen molecules [a self-assembled mono-layer of octadecanethiol on gold bottom electrodes] and opens the door for studying a wide variety of organothiol candidates for molecular electronics. The fabrication scheme is designed in a way that it can be modified into all-carbon devices in the future by using graphitic carbon bottom electrodes functionalized with nitrozoabenzene, for example, and MWCNTs or graphene as the top electrodes. Alternatively, the scheme is applicable for all-gold devices with gold bottom electrodes and gold nanowire top electrodes.

Diameter-Dependent Bending Modulus of Individual Multiwall Boron Nitride Nanotubes

Renato Pinto Reveggino

Modulus-BNNTs-2013

The mechanical properties of individual multi-wall boron nitride nanotubes (MWBNNTs) synthesized by a growth-vapor-trapping chemical vapor deposition method are investigated by a three-point bending technique via atomic force microscopy. Multiple locations on suspended tubes are probed in order to determine the boundary conditions of the supported tube ends. The bending moduli (EB) calculated for 20 tubes with diameters ranging from 18 to 58 nm confirm the exceptional mechanical properties of MWBNNTs, with an average EB of 760 ± 30 GPa. For the first time, the bending moduli of MWBNNTs are observed to increase with decreasing diameter, ranging from 100 ± 20 GPa to as high as 1800 ± 300 GPa. This diameter dependence is evaluated by Timoshenko beam theory. The Young’s modulus and shear modulus were determined to be 1800 ± 300 and 7 ± 1 GPa, respectively, for a trimmed data set of 16 tubes. The low shear modulus of MWBNNTs is the reason for the detected diameter-dependent bending modulus and is likely due to the presence of interwall shearing between the crystalline and faceted helical nanotube structures of MWBNNTs.

Low-temperature synthesis of indium tin oxide nanowires as the transparent electrodes for organic light emitting devices

Renato Pinto Reveggino

ITO-NWs-OLEDs-Nanotech2012

Low-temperature growth of indium tin oxide (ITO) nanowires (NWs) was obtained on catalyst-free amorphous glass substrates at 250 ◦C by Nd:YAG pulsed-laser deposition. These ITO NWs have branching morphology as grown in Ar ambient. As suggested by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM), our ITO NWs have the tendency to grow vertically outward from the substrate surface, with the (400) plane parallel to the longitudinal axis of the nanowires. These NWs are low in electrical resistivity (1.6 × 10−4 cm) and high in visible transmittance (∼90–96%), and were tested as the electrode for organic light emitting devices (OLEDs). An enhanced current density of ∼30 mA cm−2 was detected at bias voltages of ∼19–21 V with uniform and bright emission. We found that the Hall mobility of these NWs is 2.2–2.7 times higher than that of ITO film, which can be explained by the reduction of Coulomb scattering loss. These results suggested that ITO nanowires are promising for applications in optoelectronic devices including OLED, touch screen displays, and photovoltaic solar cells.

Pulsed laser deposition of indium tin oxide nanowires in argon and helium

Renato Pinto Reveggino

ITO-NWs-MatLett2012

Nanowires of indium tin oxide (ITO) were grown on catalyst-free amorphous glass substrates at relatively low temperature of 250 °C in argon and helium ambient by the Nd:YAG pulsed laser deposition technique. All the ITO samples showed crystalline structure due to substrate heating and the (400) X-ray diffraction peak became relatively stronger as the pressure was increased. The surface morphology was also changed from compact, polycrystalline thin-film layers to a dendritic layer consisting of nanowires for some limited pressure ranges. The transition from the normal thin-film structure to nanowires was likely due to the vapor–liquid–solid mechanism but under catalyst-free condition. These nanowires tended to grow perpen-dicularly on the glass substrate, as observed with the transmission electron microscopy (TEM), which also confirmed that these nanowires were crystalline.

Ice nucleation at the contact line triggered by transient electrowetting fields

Renato Pinto Reveggino

IceNucleation-APL2015

Supercooled water is found to have a significantly enhanced freezing temperature during transientelectrowetting with electric fields of order 1 V/lm. High speed imaging reveals that the nucleationoccurs randomly at the three-phase contact line (droplet perimeter) and can occur at multiple points during one freezing event. Possible nucleation mechanisms are explored by testing various substrate geometries and materials. Results demonstrate that electric field alone has no detectable effect on ice nucleation, but the moving boundary of the droplet on the substrate due to electrowetting is associated with the triggering of nucleation at a much higher temperature. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4938749]