Black phosphorus reveals its secrets

Researchers from Université de Montréal, Polytechnique Montréal and the Centre national de la recherche scientifique (CNRS) in France have succeeded in preventing two-dimensional layers of black phosphorus from oxidising. By doing so, they have opened the doors to exploiting their striking properties in a number of electronic and optoelectronic devices.

Black phosphorus, a stable allotrope of phosphorus that presents a lamellar structure similar to that of graphite, has recently begun to capture the attention of physicists and materials researchers. It is possible to obtain single atomic layers from it, which researchers call 2D phosphane. A cousin of the widely publicised graphene, 2D phosphane brings together two very sought-after properties for device design.

First, 2D phosphane is a semiconductor material that provides the necessary characteristics for making transistors and processors. With its high mobility, it is estimated that 2D phosphane could form the basis for electronics that are both high performance and low cost.

Furthermore, this new material features a second, even more distinctive, characteristic: its interaction with light depends on the number of atomic layers used. One monolayer will emit red light, whereas a thicker sample will emit into the infrared. This variation makes it possible to manufacture a wide range of optoelectronic devices, such as lasers or detectors, in a strategic fraction of the electromagnetic spectrum.

Until now, the study of 2D phosphane’s properties was slowed by a major problem: in ambient conditions, very thin layers of the material would degrade, to the point of compromising its future in the industry despite its promising potential.

As such, the research team has made a major step forward by succeeding in determining the physical mechanisms at play in this degradation and in identifying the key elements that lead to the layers’ oxidisation.

“We have demonstrated that 2D phosphane undergoes oxidisation under ambient conditions, caused jointly by the presence of oxygen, water and light. We have also characterised the phenomenon’s evolution over time by using electron beam spectroscopy and Raman spectroscopy,” reports Professor Richard Martel of Université de Montréal's Department of Chemistry.

Next, the researchers developed an efficient procedure for producing these very fragile single-atom layers and keeping them intact.

“We were able to study the vibration modes of the atoms in this new material. Since earlier studies had been carried out on heavily degraded materials, we revealed the as-yet-unsuspected effects of quantum confinement on atoms’ vibration modes,” noted Professor Sébastien Francoeur of Polytechnique’s Department of Engineering Physics.

The study’s results have been published in the journal Nature Materials. The results are expected to help the world scientific community develop 2D phosphane’s very special properties with the aim of developing new nanotechnologies that could give rise to high-performance microprocessors, lasers, solar cells and more.

This work is financially supported by the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation and Fonds de Recherche du Québec-Nature et technologie