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

Glucose Biosensors Based on Vertically-Aligned Multi-walled Carbon Nanotubes

July 1, 2017 Renato Pinto Reveggino

Glucose-MRS2010

Vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs) were grown using plasma

enhanced chemical vapor deposition (PECVD) technique. These VA-MWCNTs were then dip

coated by Poly methyl methacrylate (PMMA) followed by annealing. Samples were then

polished to expose the tips of CNTs. Biological molecules Glucose Oxidase (GOx) were then

immobilized on the exposed tips of these nanoelectrode ensembles. Here we present further

characterization of these devices, with results on the detection limits and measurement stability.

We found that these sensors can be reused for longer than six months when kept in proper

storage conditions.

Comparing Field Emission Stability of Lithography-free, Modified Multi-Walled Carbon Nanotubes

June 18, 2017 Renato Pinto Reveggino

FE-MRS2010

Field emission from carbon nanotubes (CNTs) has been known for more than a decade but there is no commercialized product available in the market. Apparently, we need to improve our basics understanding on stable field emission from CNTs. Here we compared the field emission properties of as grown vertically-aligned multi-walled carbon nanotubes (MWCNTs) to two types of modified MWCNTs: 1) Conical bundles of opened-tip MWCNTs, and 2) Opened-
tip MWCNTs embedded in poly-methyl methacrylate (PMMA). We found that both types of modified MWCNTs have lower emission thresholds and better emission stability than the as grown samples. Among these modified samples, MCNTs embedded in PMMA has lower emission thresholds and better emission stability. We attributed these improvements to the filling of spacing between MWCNTs with PMMA that has higher dielectric constant than vacuum.

Enhanced field emission stability and density produced by conical bundles of catalyst-free carbon nanotubes

June 18, 2017 Renato Pinto Reveggino

FE-carbon2010

Self-assembled bundling and catalyst removal can enhance the field emission stability and density of vertically-aligned multiwalled carbon nanotubes (VA-MWCNTs). These catalyst-free, opened tip, VA-MWCNTs offered better emission stability than the as grown samples. Both the emission stability and density were further enhanced as the opened-tip MWCNTs self-assembled into arrays of conical bundles. Theoretical simulation suggests that higher emission density was due to the reduced screening effects. The simulated local fields at the tips of the bundles suggest for a two-order of magnitude lower electric field loading on MWCNTs and contribute to prolong emission stability needed for practical applications.

Stable Electron Field Emission from PMMACNT Matrices

June 18, 2017 Renato Pinto Reveggino

FE-ACS_Nano2010

We have created PMMACNT matrices by embedding opened-tip vertically aligned multiwalled

carbon nanotubes (VA-MWCNTs) with poly(methyl methacrylate) (PMMA). These PMMACNT matrices are

excellent electron field emitters with an emission threshold field of 1.675 V/m, more than 2-fold lower that

that of the as-grown sample. In addition, the emission site density from these matrices is high, merely filling up

the entire sample surface. Emission stability test at 1.35 mA/cm2 was performed continuously for 40 h with no

significant degradation. On the basis of our theoretical simulation and hypothetical modeling, we attribute these

performances to the reduced screening effect and fewer Joule heatings due to the shorter effective transport

distance of the electrons in MWCNTs.

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

June 17, 2017 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.