China University of Science and Technology, Hefei National Laboratory of Microscale Physical Sciences and Physics, Professor Qiao Zhenhua and Nanjing University Professor Miao Feng, Professor Wang Bergen cooperation in multilayer piezoelectric graphene made significant progress in the study, the first experimentally observed graphene Material system in the positive piezoelectric effect, and theoretically reveals the multilayer structure of the inner layer of the interaction between the significant contribution to this effect. The research was published online in Nature Communications on September 11 titled "The positive piezoconductive effect in graphene." Wang Ke, a Ph.D. student in the research group at Qiao Zhenhua, co-authored the paper.
Graphene is a monatomic layer of carbon material, first obtained by Geim and Novoselov in 2004 by the mechanical lift-off method, and as the first real two-dimensional system began an era of two-dimensional material research. Due to the very superior mechanical, electrical and magnetic properties of graphene, many physicists in the field of condensed matter physics have quickly attracted the attention. Among them, the excellent elasticity of graphene makes mechanics an effective means of regulation and made a series of progress, such as experimentally observed stress-induced pseudo-magnetic field up to 300 Tesla. More theoretical predictions, such as stress-induced quantum Hall effect, superconductivity, etc., have yet to be more determined experimental verification. In addition, how to control electron transport properties by mechanics also needs to be further studied theoretically and experimentally. Previous studies have found that single-layer graphene can achieve a negative piezoelectric effect. Professor Qiao Zhenhua and Nanda collaborators found that, unlike single-layer graphene, double-layer and multi-layer graphene can achieve positive piezoelectric conductivity. Under the external stress, the carbon atom spacing in single-layer graphene increases, and the energy of the neighboring transition decreases. As a result, the electron Fermi velocity becomes smaller and further the conductance decreases, resulting in a negative piezoelectric effect. However, in multilayer graphene, the external stress not only lengthens the in-plane carbon atom spacing but also reduces the interlayer spacing of graphene, resulting in an increase of the inter-layer carbon atoms' transition energy, and more importantly, the interaction between the layers Lattice can be amended. This correction causes a change in the Fermi surface in the compression zone, increasing the conductance of the channel, thereby enhancing the conductance of the positive piezo-electric conductivity. The combination of experiment and theory well explains this counterintuitive physical phenomenon given by the interaction between layers. The research not only deepens the understanding of the mechanical and electrical properties of graphene systems, but also helps to explore its applications in nano-electromechanical systems and flexible electronic devices.
The research was supported by the National Natural Science Foundation of China, the "Hundred Talents Program" of Chinese Academy of Sciences, the "Youth Thousand Talents Program" of the Central Organization Department, the "2011 Plan" of the Ministry of Education and the Natural Science Foundation of Anhui Province. China Transtech Services Supercomputing Center also gave the crucial support to the completion of this work.
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