New properties of graphene explored

A potential new revolution in technology

UA researchers have recently documented the unique temperature-propagation properties of graphene, a carbon-based substance possessing profound potential in the fields of electronics and biological engineering. Heat diffusion through a material had long been considered an unalterable process — that is, until the isolation and study of graphene.

People are not strangers to the type of carbon found in graphene; in fact, it is commonly found in pencil lead. Graphene itself is a hexagonal lattice of carbon atoms, with each point in the structure containing a single carbon atom. The whole framework is only one atom thick.

“Graphene is a two-dimensional material composed of a single sheet of carbon atoms,” said Justin Bergfield, a postdoctoral fellow at Northwestern University. “What is truly remarkable is that, unlike an electron in free space, the electrons confined to a piece of graphene have a relationship between their velocity and energy which is like that of light.”

In other words, the electrons, negatively charged particles that make up atoms, move at a speed of 1 million meters per second between carbon atoms in graphene, Bergfield explained.

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In traditional electrical conductors like copper, electrons travel only a few nanometers before scattering from a defect or excitation, which sends them off in a random direction.

“Heat is conducted ‘ballistically’ by both quantum electron waves and quantum sound waves … in graphene,” explained Charles Stafford, a physics professor at the UA. “These waves can travel rapidly for distances of up to a micrometer or more before scattering. This is very different from the behavior of typical materials, where heat diffuses slowly from one point to another as a result of the random motions of electrons carrying the heat.”

The organized wave-like flow of electrons in graphene allows for the formation of intricate wave formations which lead to hot and cold spots, the temperature of which can be quantified using a scanning tunneling microscope-like thermometer, Bergfield said.

“Hot spots and cold spots up to tens of nanometers across can persist indefinitely within the heat flow of graphene, somewhat like an eddy that can persist in a flowing river,” Stafford said.

Graphene’s remarkable conductivity, flexibility, durability, strength (more than 100 times stronger than steel) and unusual heat properties are unlocking the vault to new potential technologies such as foldable touchscreens for smartphones and tablets, plastics with better conductivity than metals and electronic devices with greater efficiency and twice the power.

Since one of the major obstacles with electronics is overheating, graphene may prove to be a great advantage in circumventing this issue because it is possible to control where heat is localized on a nanoscale level, Stafford said.

“The crests of the electron waves are the hot spots and the dips are the cold spots, the locations of which can be predicted by solving the quantum wave equation for the electrons,” Stafford said. “The wave patterns of hot and cold spots can be controlled by tuning the wavelength of the electron waves using a gate voltage.”

This ability to manipulate the physical world at the nanoscale level foreshadows a potential technological revolution, the efficiency and advancement of which could end up transforming everyday life.

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