photo by: David F McKinney/KU University Relations

The University of Kansas' Ultrafast Laser Lab is pictured.

A discovery made by researchers with an ultrafast laser at the University of Kansas might help our electronics and other such devices work at ultrafast speeds in the future.

A substance kind of similar to pencil lead may play a role too.

KU researchers this month had new work published in the scientific journal ACS Nano that is being billed as another discovery that could lead to breakthroughs in semiconductors, which are fundamental components for a host of electronics, information technology and energy devices.

The new research determined that electrons can move at “ballistic” speeds when in a substance called “graphene.”

The research was conducted at KU’s Ultrafast Laser Lab by Ryan Scott, a doctoral student in KU’s Department of Physics & Astronomy, and under the mentorship of Hui Zhao, a professor in the department.

Zhao said in a KU press release that electronic devices that utilize “ballistic transport” to move electrons could potentially be faster, more powerful and more energy efficient.

It appears, though, that a key to securing those types of improvements could be to build semiconductors using graphene, rather than more common materials like silicon. Graphene has been a great curiosity of scientists since it was discovered in 2004. As its name suggests, graphene indeed is a substance that is extracted from graphite, which is the material found at the end of most pencils.

The scientists who discovered graphene won a Nobel Prize in Physics in 2010 as the potential of the substance became clearer. Today, companies are promoting graphene as a material that is 200 times stronger than steel and five times lighter than aluminum.

But less understood has been graphene’s potential as a semiconductor. Zhao has been studying the material for years. In 2018, KU announced that he and other researchers at the university had made discoveries that could result in graphene being used to produce ultrathin and flexible solar panels that operate at high efficiencies.

The latest KU research continues to focus on how electrons move within graphene, and how they can be made to move faster and more efficiently.

“Current electronic devices, such as computers and phones, utilize silicon-based field-effect transistors,” Zhao said. “In such devices, electrons can only drift with a speed on the order of centimeters per second due to the frequent collisions they encounter. The ballistic transport of electrons in graphene can be utilized in devices with fast speed and low energy consumption.”

Researchers had suspected that electrons could move in graphene fast enough to achieve what researchers call “ballistic transport,” which they describe as a state where an electron moves freely, quickly and without collision, much like a ballistic missile travels through the air.

However, researchers couldn’t know for sure that electrons were moving at such speeds in graphene because previous measurement techniques “aren’t fast enough to trace the electrons as they move,” Scott said in a KU press release.

Researchers had only about one-trillionth of a second to measure “super-light electrons” in graphene. To address that problem, Scott and KU researchers developed a new structure to make measurements more feasible. In layman’s terms, the researchers figured out how to use two layers of graphene, along with two layers of other materials, to separate electrons.

“Separating them with two layers of molecules, with a total thickness of just 1.5 nanometers, forces the electrons to stay mobile for about 50-trillionths of a second, long enough for the researchers, equipped with lasers as fast as 0.1 trillionth of a second, to study how they move,” Scott said in a KU press release.

Still no easy task, and KU researchers conducted experiments with some mind-bending numbers. The researchers “liberated” 20,000 electrons at once and used a probe laser to measure light reflection. Researchers repeated the process 80 million times for each data point, according to the KU press release.

They found the electrons, on average, move ballistically for about 20 trillionths of a second with a speed of 22 kilometers per second before running into something that terminates their ballistic motion.

The research was funded by a grant from the Department of Energy under the program of Physical Behavior of Materials.

Zhao said currently his lab is working to refine their material design to guide electrons more efficiently to the desired graphene layer, and trying to find ways to make them move longer distances ballistically.

— KU News Service contributed to this report.