Frontiers in Energy Research: Frontiers in Energy Research: Summer 2016

Electrical Conductivity Control Through Mechanical Bending

First principles calculations assist in new materials design

Crystal structures of 2D materials: (a) molybdenum disulfide, (b) phosphorene, and (c) graphene. In (d) a diagram of the bending is shown, where the nanoribbon has length d0 before bending and d after bending. Adapted with permission from Nano Letters (see reference below). Copyright 2016 American Chemical Society.

Mechanical bending affects the distribution of the charges, causing charge localization, as indicated with blue color in (a) molybdenum disulfide and (b) phosphorene. This means that the electrical conductivity is affected and it can be controlled or even be turned on and off through bending of the material. Adapted with permission from Nano Letters (see reference below). Copyright 2016 American Chemical Society.

If we blew up an atom about a quarter million times, it would be the size of a golf ball! That’s how small an atom is. Researchers, however, have made it possible to work with materials that are as thick as one or just a few atoms. These materials are called 2D (two-dimensional) materials because effectively one of their dimensions is really small. Two-dimensional materials have been of increasing interest, because of their unusual characteristics and interesting properties such as exceptional strength and flexibility, and good thermal and electrical conductivity. These properties make them popular in a wide range of applications, including nanoelectronics for devices such as computers and cell phones, and clean energy technologies such as solar cells.

The use of 2D materials in clean energy technologies has been one of the research interests of the Center for Computational Design of Functional Layered Materials (CCDM), an Energy Frontier Research Center at Temple University. Some of the latest findings of Liping Yu, Adrienn Ruzsinszky, and John Perdew on 2D materials research connect the mechanical bending of the materials to their electrical properties by using first principles calculations. First principles methods are based on fundamental physics laws and provide detailed information of the mechanical, optical, and electrical properties of materials. Starting from the atomic structure and with description of the motion and interaction of subatomic particles, the physical and chemical properties of the materials can be determined, without making any assumptions.

This research team, uses electronic structure calculations to relate mechanical properties, such as stress and bending energy, to the electrical properties of the material. They study the bending effects in nanoribbons of a single atomic layer, two-atomic layer, and three-atomic layer materials: graphene, phosphorene, and molybdenum disulfide, respectively. Their findings show that in molybdenum disulfide and phosphorene, bending can affect the distribution of the charges in the materials, causing charge localization. The charge localization can be controlled; therefore, the conductivity of molybdenum disulfide and phosphorene can be altered or turned on and off. Conversely, there seems to be no such effect of bending in graphene, thus making it a suitable material for applications where flexibility without other property change is required.

The researchers provide fundamental details for understanding the correlation of the properties of 2D materials, which opens the way to further technological development. The team’s results suggest that it’s possible to control the physical properties of 2D materials by mechanical bending and assist in new material design.

The researchers show that manipulating the electrical properties by applying mechanical stress and strain is possible, while they also emphasize the importance of computational methods in new material development and design and technological development.

Acknowledgments: 

This work was supported as part of the Center for the Computational Design of Functional Layered Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. The calculations were performed using resources at the National Energy Research Scientific Computing Center and National Science Foundation-supported computational resources at Temple University.

More Information: 

Yu L, A Ruzsinszky, and JP Perdew. 2016 “Bending Two-Dimensional Materials To Control Charge Localization and Fermi-Level Shift.” Nano Letters 16:2444−2449. DOI: 10.1021/acs.nanolett.5b05303

Disclaimer: The opinions in this newsletter are those of the individual authors and do not represent the views or position of the Department of Energy.

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