Ions control shape of nanofibers grown on clear substrate

Aug 16, 2011
Carbon nanofibers at the interface between non-conductive (left) and conductive (right) substrates do not align with the electrical field (E), but rather orient along the ion flux lines. Controlling the direction of the ion flux provides the means to grow oriented nanofibers even on insulating materials, thereby greatly extending the application space for this important nanoscale material. Credit: Anatoli Melechko, North Carolina State University

Researchers from North Carolina State University have found a new way to develop straight carbon nanofibers on a transparent substrate. Growing such nanofiber coatings is important for use in novel biomedical research tools, solar cells, water repellent coatings and others. The technique utilizes a charged chromium grid, and relies on ions to ensure the nanofibers are straight, rather than curling – which limits their utility.

"This is the first time, that I know of, where someone has been able to grow straight on a clear substrate," says Dr. Anatoli Melechko, an associate professor of materials science and engineering at NC State and co-author of a paper describing the research. "Such nanofibers can be used as gene-delivery tools. And a transparent substrate allows researchers to see how the nanofibers interact with cells, and to manipulate this interaction."

Specifically, the nanofibers can be coated with genetic material and then inserted into the nucleus of a cell – for example, to facilitate gene therapy research. The transparent substrate improves visibility because researchers can shine light through it, creating better contrast and making it easier to see what's going on.

The researchers also learned that play a key role in ensuring that the carbon nanofibers are straight. To understand that role, you need to know how the technique works.

This video is not supported by your browser at this time.
NC State researchers have found a new way to develop straight carbon nanofibers on a transparent substrate. Growing such nanofiber coatings is important for use in novel biomedical research tools, solar cells, water repellent coatings and others. The technique utilizes a charged chromium grid, and relies on ions to ensure the nanofibers are straight, rather than curling -- which limits their utility. Credit: Anatoli Melechko, North Carolina State University

The nanofibers are made by distributing nickel nanoparticles evenly on a substrate made of fused silicon (which is pure silicon dioxide). The substrate is then overlaid with a fine grid made of , which serves as an electrode. The substrate and grid are then placed in a chamber at 700 degrees Celsius, which is then filled with acetylene and ammonia gas. The chrome grid is a negatively charged electrode, and the top of the chamber contains a positively charged electrode.

Electric voltage is then applied to the two electrodes, creating an electric field in the chamber that excites the atoms in the acetylene and ammonia gas. Some of the electrons in these atoms break away, creating free electrons and positively charged atoms called ions. The free electrons accelerate around the chamber, knocking loose even more electrons. The positively charged ions are drawn to the negatively charged grid on the floor of the chamber.

Meanwhile, the nickel nanoparticles are serving as catalysts, reacting with the carbon in the acetylene gas (C2H2) to create graphitic carbon nanofibers. The catalyst rides on the tip of the nanofiber that forms beneath it, like a rapidly growing pillar. The term graphitic means that the nanofibers have carbon atoms arranged in a hexagonal structure – like graphite.

One problem with growing carbon nanofibers is that the surface of the catalyst can become obstructed by a carbon film that blocks catalytic action, preventing further nanofibers growth. Here's where those ions come in.

The ions being drawn to the chromium grid are moving very quickly, and they choose the shortest possible route to reach the negatively-charged metal. In their rush to reach the grid, the ions often collide with the nickel catalysts, knocking off the excess – and allowing further nanofibers growth.

Because the ions are being drawn to the chromium grid, the angle at which they strike the catalysts depends on where the catalyst is located relative to the grid. For example, if you are looking down at the grid, a catalyst just to the right of the grid will appear to be leaning right – because ions would have been striking the right side of the catalyst in an attempt to reach the grid. These nanofibers are still straight – they don't curl up – they simply lean in one direction. The bulk of the nanofibers, however, are both straight and vertically aligned.

"This finding gives us an opportunity to create new reactors for creating nanofibers, building in the chromium grid," Melechko says.

Explore further: Mirror-image forms of corannulene molecules could lead to exciting new possibilities in nanotechnology

More information: The paper, "Role of ion flux on alignment of carbon nanofibers synthesized by DC plasma on transparent insulating substrates," is forthcoming from the ACS journal Applied Materials & Interfaces.

Related Stories

New technique scales up nanofiber production

Aug 10, 2011

(PhysOrg.com) -- A new spin on an old technology will give scientists and manufacturers the ability to significantly increase their production of nanofibers, according to researchers at North Carolina State University.

Researchers create nanopatch for the heart

May 19, 2011

When you suffer a heart attack, a part of your heart dies. Nerve cells in the heart's wall and a special class of cells that spontaneously expand and contract – keeping the heart beating in perfect synchronicity ...

New fiber nanogenerators could lead to electric clothing

Feb 12, 2010

(PhysOrg.com) -- In research that gives literal meaning to the term "power suit," University of California, Berkeley, engineers have created energy-scavenging nanofibers that could one day be woven into clothing ...

Recommended for you

Tiny graphene drum could form future quantum memory

Aug 28, 2014

Scientists from TU Delft's Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential ...

Graphene reinvents the future

Aug 27, 2014

For many scientists, the discovery of one-atom-thick sheets of graphene is hugely significant, something with the potential to affect just about every aspect of human activity and endeavour.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Net Energy
not rated yet Aug 16, 2011
Materials science that I can dance to. Fascinating!