Two-dimensional (2D) materials are being the subjects of increased scientific interest, potentially improving electronic devices past the limitations of conventional silicon substrates.

Most of the modern electronics - such as small parts found in computers, cellphones, and even electric appliances - are built on integrated circuits based on silicon carriers. However, despite the increasing densities of circuits embedded in these substrates, the technology has been growing more difficult because of silicon's natural limitations.

One of the possible alternatives is the use of 2D materials - ultrathin materials about one atom thick. Among the most common of these materials is graphene, a specially-fabricated sheet from a layer of graphite. Dutch-British physicist Andre Geim and Russian-British physicist Konstantin Novoselov were awarded the 2010 Nobel Prize in Physics to discover graphene.

Although it is primarily composed of carbon atoms arranged in a honeycomb lattice arrangement, graphene has continuously fascinated researchers with its unique properties. The ultrathin material is being studied for potential applications in various fields such as energy storage, optoelectronics, composite materials engineering, catalysis, sensing, and more.

Causing 2D Materials to Vibrate

"It is important to know how they react to excitation with light," explains Professor Tobias Brixner, co-author of the study and head of Physical Chemistry I at the Julius- Maximilians- Universität (JMU) Würzburg, Bavaria, Germany. Details of their study are published in the journal Nature Communications, February 11.

Theoretically, 2D materials exhibit an electronic response similar to conventional silicon photovoltaic cells as sunlight excites them. However, the light also causes 2D sheets of graphene to vibrate in addition to its electronic response. This behavior has potential optoelectronic applications.

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This phenomenon is a previously-undiscovered behavior among 2D materials, especially at room temperature. With the international study including Tobias Brixner and collaborators, they succeeded in understanding the properties of this light-induced oscillation excitation in 2D materials, particularly in a transition metal dichalcogenide, under room temperature conditions.

Brixner adds in a JMU press release that the behavior is technically known as "exciton-phonon coupling strength. He adds that this is hard to identify since, at room temperature, the absorption spectrum is mostly "smeared out" where no individual spectrum lines are distinguishable.

Observations Made Through Novel Microscopy

To achieve their latest observations, researchers used a coherent 2D microscopy method, developed by Dr. Donghai Lin, also an author of the study from Universität Würzburg. Through this technique, researchers use the spatial resolution of a microscope together with femtosecond range time resolutions of ultra-short laser pulses, both combined with multi-dimensional frequency resolution. With coherent 2D microscopy, researchers were able to quantify the effect of oscillations.

"Surprisingly, it turned out that the exciton-phonon coupling strength in the investigated material is much greater than in conventional semiconductors," Brixner adds. "This finding is helpful in the further development of 2-D materials for specific applications."

Also known as single-layer materials, 2D materials have found potential applications in a variety of fields. While still in their infancy, 2D materials have been investigated with regard to how they affect biological cells and tissues for potential use in drug delivery and injury recovery.

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