Theoretical studies show that carbon nanotubes, if packed closely enough together, should be able to outperform copper as an electrical conductor. But because of the way carbon nanotubes are grown – in sparse nanoscale “forests” where carbon molecules compete for growth-inducing catalysts – scientists have been unable to successfully grow tightly packed bundles.
James Jiam-Qiang Lu, associate professor of physics and electrical engineering at Rensselaer, together with his research associate Zhengchun Liu, decided to investigate how to “densify” carbon nanotube bundles after they are already grown. He detailed the results of the post-growth densification project on June 6 at the Institute of Electrical and Electronics Engineers’ International Interconnect Technology Conference (IITC) in Burlingame, Calif.
Lu’s team discovered that by immersing vertically grown carbon nanotube bundles into a liquid organic solvent and allowing them to dry, the nanotubes pull close together into a dense bundle. Lu attributes the densification process to capillary coalescence, which is the same physical principle that allows moisture to move up a piece of tissue paper that is dipped into water.
The process boosts the density of these carbon nanotube bundles by five to 25 times. The higher the density, the better they can conduct electricity, Lu said. Several factors, including nanotube height, diameter, and spacing, affect the resulting density, Liu added. How the nanotubes are grown is also an important factor that impacts the resulting shape of the densified bundles.
Images of the experiment are more striking than any “before and after” photos of the latest fad diet. In one instance, Liu started with a carbon nanotube bundle 500 micrometers in diameter, shaped somewhat like a marshmallow, and dipped it into a bath of isopropyl alcohol. As the alcohol dried and evaporated, capillary forces drew the nanotubes closer together. Van Der Waals forces, the same molecular bonds that boost the adhesion of millions of setae on gecko toes and help the lizard defy gravity, ensure the nanotubes retain their tightly packed form.
The resulting bundle shrunk to a diameter of 100 micrometers, with a 25-fold increase in density. Instead of a marshmallow, it looked more like a carpenter’s nail.
“It’s a significant and critical step toward the realization of carbon nanotube interconnects with better performance than copper,” Lu said of his research findings. “But there’s still a lot of work to do before this technology can be integrated into industrial applications.”
Despite his initial successes, Lu said the density results obtained are not ideal and carbon nanotubes would have to be further compacted before they can outperform copper as a conductor. A close-up photo, taken using a scanning electron microscope, reveals there are still large empty spaces between densified nanotubes. The research team is exploring various methods to achieve ever-higher density and higher quality of carbon nanotube bundles, he said.
Lu is confident that these densified carbon nanotubes, with their high conductivity, ability to carry high current density, and resistance to electromigration, will be key to the development of 3-D computer chips. Chips used today can only shrink so much smaller, as their flat surface must have enough room to accommodate scores of different components. But the semiconductor industry and academia are looking at ways to layer chip components into a vertical stack, which could dramatically shrink the size of the overall chip.
Densified carbon nanotubes, with their ends trimmed and polished, can be the basic building blocks for interconnects that would link the stacked layers of a 3-D computer chip, Lu said.
“Carbon nanotubes are one of the most promising materials for interconnects in 3-D integration,” he said. Other potential applications of the densified nanotubes are high surface area electrodes for supercapacitors, fuel cell electrodes for hydrogen storage, heat dissipation materials for thermal conductors, and other situations that require high electrical, thermal, or mechanical performance.
Michael Mullaney | EurekAlert!
Fluorescent holography: Upending the world of biological imaging
25.10.2016 | Colorado State University
Did you know that infrared heating is an essential part of automotive manufacture?
25.10.2016 | Heraeus Noblelight GmbH
Ultrafast lasers have introduced new possibilities in engraving ultrafine structures, and scientists are now also investigating how to use them to etch microstructures into thin glass. There are possible applications in analytics (lab on a chip) and especially in electronics and the consumer sector, where great interest has been shown.
This new method was born of a surprising phenomenon: irradiating glass in a particular way with an ultrafast laser has the effect of making the glass up to a...
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
25.10.2016 | Earth Sciences
25.10.2016 | Power and Electrical Engineering
25.10.2016 | Process Engineering