In a collaborative and multidisciplinary study, scientists develop methods to explore phosphorene and its properties.
Phosphorene, discovered in 2014, is related to the two-dimensional graphene and has been established to have numerous photonic applications. The majority of these properties, however, is its capacity for anisotropic electron conduction. This means that its electron conduction property changes depending on the crystal orientation.
Researchers from Tohoku University, Massachusetts Institute of Technology, University of Pennsylvania, Oak Ridge National Library and Rensselaer Polytechnic Institute (RPI) worked together to develop a method that would accurately identify the crystal orientation by using the light and electron interaction within the phosphorene.
Phosphorene is an interesting material, which has properties that change depending on the direction of how things are done, said Vincent Meunier, head of Rensselaer Deparment of Physics, Applied Physics, and Astronomy.
Meunier, who is also a member of the RPI Center for Materials, Devices, and Integrated Systems (cMDIS), said that because phosphorene is a relatively new material, its intrinsic properties must be properly understood.
To predict crystal orientation, the team used Raman spectroscopy to investigate the atomic vibrations within the crystal while electron-phonon interaction energy passes through it. Initial results showed inconsistencies, which led the researchers to use actual images of the sample crystal orientation using Transmission Electron Microscopy (TEM).
Images were then compared with those of the Raman spectroscopy and showed that prediction of crystal orientation is not due to electron-phonon interactions.
Meunier explained that Raman spectroscopy uses laser to deliver energy towards the phosphorene that causes it to vibrate intrinsically. However, lighting the material from different directions would produce varying results because of the electron and light interaction within the material. With this, the electron-photon interaction, in itself, is anisotropic as well.
Despite revealing flawed Raman spectra interpretations of electron-phonon interactions, Meunier believes that electron-photon interactions, by itself, can provide accurate predictions of the orientation of the crystal.
"[I]t turns out that it's not so easy to use Raman vibrations to find out the direction of the crystal," said Meunier. "But, and this is the beautiful thing, what we found is that the electron-photon interaction (which can be measured by recording the amount of light absorbed) — the interaction between the electrons and the laser — is a good predictor of the direction.
Through this, the behavior of phosphorene can be predicted as a result of an external stimulus.
The study was published online in ACS Nano Letters on March 10.