‘On-Demand ‘ Nanotube Forests’ for Electronics Fabrication


Nanotube Forrests 042116 id43200A system that uses a laser and electrical current to precisely position and align carbon nanotubes represents a potential new tool for creating electronic devices out of the tiny fibers.
 

Because carbon nanotubes have unique thermal and electrical properties, they may have future applications in electronic cooling and as devices in microchips, sensors and circuits. Being able to orient the carbon nanotubes in the same direction and precisely position them could allow these nanostructures to be used in such applications.

However, it is difficult to manipulate something so small that thousands of them would fit within the diameter of a single strand of hair, said Steven T. Wereley, a professor of mechanical engineering at Purdue University.
“One of the things we can do with this technique is assemble carbon nanotubes, put them where we want and make them into complicated structures,” he said.

 

This graphic illustrates a system that uses a laser and electrical field to precisely position and align carbon nanotube
This graphic illustrates a system that uses a laser and electrical field to precisely position and align carbon nanotubes, representing a potential new tool for assembling sensors and devices out of the tiny nanotubes and nanowires. The two microscope images at the bottom show the nanotubes aligned (left) and returning to their random orientation after the electric field and laser were turned off. (Image: Avanish Mishra and Steven Wereley)
New findings from research led by Purdue doctoral student Avanish Mishra are detailed in a paper that has appeared online March 24 in the journal Microsystems and Nanoengineering (“Dynamic optoelectric trapping and deposition of multiwalled carbon nanotubes”).
The technique, called rapid electrokinetic patterning (REP), uses two parallel electrodes made of indium tin oxide, a transparent and electrically conductive material. The nanotubes are arranged randomly while suspended in deionized water. Applying an electric field causes them to orient vertically. Then an infrared laser heats the fluid, producing a doughnut-shaped vortex of circulating liquid between the two electrodes. This vortex enables the researchers to move the nanotubes and reposition them.
“When we apply the electric field, they are immediately oriented vertically, and then when we apply the laser, it starts a vortex, that sweeps them into little nanotube forests,” Wereley said.
The research paper was authored by Mishra; Purdue graduate student Katherine Clayton; University of Louisville student Vanessa Velasco; Stuart J. Williams, an assistant professor of mechanical engineering at the University of Louisville and director of the Integrated Microfluidic Systems Laboratory; and Wereley. Williams is a former doctoral student at Purdue.
The technique overcomes limitations of other methods for manipulating particles measured on the scale of nanometers, or billionths of a meter. In this study, the procedure was used for multiwalled carbon nanotubes, which are rolled-up ultrathin sheets of carbon called graphene. However, according to the researchers, using this technique other nanoparticles such as nanowires and nanorods can be similarly positioned and fixed in vertical orientation.
The researchers have received a U.S. patent on the system.
The experimental work was performed at the Birck Nanotechnology Center in Purdue’s Discovery Park. Future research will explore using the technique to create devices.
Source: By Emil Venere, Purdue University

 

Better fighter planes, space shuttles on the way, thanks to new research


FULL STORY

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A team of scientists led by Changhong Ke, associate professor of mechanical engineering at Binghamton University’s Thomas J. Watson School of Engineering and Applied Science, and researcher Xiaoming Chen were the first to determine the interface strength between boron nitride nanotubes (BNNTs) and epoxy and other polymers.

“We think that this could be the first step in a process that changes the way we design and make materials that affect the future of travel on this planet and exploration of other worlds beyond our own,” said Ke. “Those materials may be way off still, but someone needed to take the first step, and we have.”

 

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Ke’s group found that BNNTs in polymethyl metacrylate (PMMA) form much stronger interfaces than comparable carbon tubes with the same polymer. Furthermore, BNNT-epoxy interfaces are even stronger. A stronger interface means that a larger load can be transferred from the polymer to nanotubes, a critical characteristic for superior mechanical performance of composite materials. Future airplane wings and spacecraft hulls built of those BNNT composite materials could be lighter and more fuel efficient, while maintaining the strength needed to withstand the rigors of flight.

Since nanotube wall thickness and diameters are measured in billionths of a meter, Ke and Chen extracted single BNNTs from a piece of epoxy and then repeated the process with PMMA inside an electron microscope. Their conclusions were based on the amount of force needed to do the extractions. This was the first time that BNNTs –more chemically and thermally stable than the more common carbon nanotubes (CNTs) –were in this kind of experiment. BNNTs can shield space radiation better than CNTs, which would make them an ideal building material for spacecraft.

“They are both light and strong,” Ke said of the two kinds of tubes. “They have similar mechanical properties, but different electrical properties. Those differences help to add strength to the BNNT interfaces with the polymers.”

Metaphorically, think of the epoxy or other polymer materials with the BNNT nanotubes inside like a piece of reinforced concrete. That concrete gets much of its strength from the makeup of the steel rebar and cement; the dispersion of rebar within the cement; the alignment of rebar within the cement; and “stickiness” of the connection between the rebar and the surrounding cement. The scientists essentially measured the “stickiness” of a single nanotube ‘rebar’ — helped by molecular and electrostatic interactions — by removing it from polymer “cement.”

The work was funded by the US Air Force Office of Scientific Research — Low Density Materials program, with materials provided by NASA. Co-authors Xianqiao Wang and graduate student Liuyang Zhang from the University of Georgia provided verification and explanation data through computational simulations after the experiments were conducted in Binghamton.

Catharine Fay from the NASA Langley Research Center and Cheol Park of the Center and the University of Virginia are co-authors on the paper.

In September, Ke and his collaborators received three years of additional funding totaling $815,000 from the Air Force to continue research.

The paper, “Mechanical Strength of Boron Nitride Nanotube-Polymer Interfaces,” was published in the latest issue of Applied Physics Letters.


Story Source:

The above post is reprinted from materials provided by Binghamton University. Note: Materials may be edited for content and length.


Journal Reference:

  1. Xiaoming Chen, Liuyang Zhang, Cheol Park, Catharine C. Fay, Xianqiao Wang, Changhong Ke. Mechanical strength of boron nitride nanotube-polymer interfaces. Applied Physics Letters, 2015; 107 (25): 253105 DOI: 10.1063/1.4936755

Nanowires: Major Building-block for Nanotechnology Devices: Transistors, Solar Cells, Lasers and More


By Michael Berger. Copyright © Nanowerk

201306047919620(Nanowerk Spotlight) Nanowires are considered a major  building block for future nanotechnology devices, with great potential for  applications in transistors, solar cells, lasers, sensors, etc.

 

*** Read articles explaining how ‘nanowires and nanotubes’ differ from other quantum materials, such as quantum dots, and their potential applications here:

http://www.nanowerk.com/news2/newsid=29945.php

http://www.nanowerk.com/news/newsid=16857.php

 

Now, for the first time, nanotechnology researchers have  utilized nanowires as a ‘storage’ device for biochemical species such as ATP.   Led by Seunghun Hong, a professor of physics, biophysics and chemical  biology at Seoul National University, the team developed a new nanowire  structure – which they named ‘nano-storage wire’ – which can store and release  biomolecules.

Reporting their findings in the July 16, 2013 online edition of  ACS Nano (“Nano-Storage Wires”), Hong’s group demonstrated  that their nano-storage wire structure can be deposited onto virtually any  substrate to build nanostorage devices for the real-time controlled release of  biochemical molecules upon the application of electrical stimuli.

“Our nano-storage wires are multisegmented nanowires comprised  of three segments and each segment plays a role in extending the applications of  the nanowire,” Hong explains to Nanowerk: “1) the conducting polymer segment  stores biomolecules; 2) the nickel segment allows the utilization of magnetic  fields to drive the nanowires and place them onto a specific location for device  applications; and 3) the gold segment enables a good electrical contact between  the deposited nano-storage wires and the electrodes. The polymer segment is  utilized for the controlled release of ATP molecules. The nickel segment enables  the magnetic localization of nano-storage wires, while the gold segment provides  a good electrical contact with electrodes.”

  nano-storage wire Left:  Schematics of a nano-storage wire. Right: SEM image of a single nano-storage  wire. The dark, intermediate, and bright regions represent PPy-ATP (conducting  polymer with ATP molecules), nickel, and gold segments, respectively. (Images:  Dr. Seunghun Hong, Seoul National University)   

The released biomolecules from such a nanowire-storage system  can be used for instance to control the activity of biosystems. As a proof of  concept, the researchers stored ATP in their nano-storage wires and released it  by electrical stimuli, which activated the motion of motor protein systems.   The team also demonstrated flexible nanostorage devices. Here,  nano-storage wires were driven by magnetic fields and deposited onto nickel/gold  films on a transparent and flexible polyimide film. The device transmitted some  light, and it can be easily bent.   They also showed that the nanowires could be deposited onto  curved surfaces such as the sharp end of a micropipet.

nano-storage wires deposited on tip of a micropipette

SEM  image of nano-storage wires deposited on a micropipet. (Reprinted with  permission from American Chemical Society)   

“Such probe-shaped storage devices can be used for the delivery  of chemicals to individual cells through a direct injection,” says Hong.  “Basically, our results show that nano-storage wires are quite versatile  structures and we can deposit them onto virtually any structure to create  nanoscale devices for the controlled release of biochemical materials.”   “Nano-storage wires will allow the fabrication of advanced  biochips which can activate or deactivate the activities of biosystems in real  time,” Hong points out. “The activation and deactivation of biosystems such as  biomotors, are controlled by specific biomolecules.

In our method, we can  selectively control the biomolecular activities related with ATP or any released  chemical species while leaving other biomolecular activities unaltered.”   Having demonstrated the storage of ATP, the team is now planning  to store other biomolecules in our nano-storage wires. Examples are drugs to  control the activity of cells and tissues, enzymes to activate specific signal  pathways in biosystems etc.   “Eventually, we would like to build an advanced biochip which  can be utilized to control the activities of desired biosystems in real-time,”  says Hong.

By Michael Berger. Copyright © Nanowerk

Read more: http://www.nanowerk.com/spotlight/spotid=31619.php#ixzz2apWtDi34