Phonon anharmonicity and thermal transport in two-dimensional materials
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2018-01-01 |
| Journal | RWTH Publications (RWTH Aachen) |
| Authors | Guangzhao Qin, Ming Hu, Jochen M. Schneider |
Abstract
Section titled āAbstractāThe thesis focuses on the phonon an harmonicity and thermal transport in two dimensional(2D) materials. Firstly, the selection of options and parameters involved in the methodology are discussed in detail based on an application example of graphene, with the topic focusing on the effect of different exchange-correlation functionals. Regarding to the calculations of thermal conductivity (), a strategy developed in the framework of phonon Boltzmann transport equation (BTE) coupled with first-principles calculations is presented, which can be used to efficiently accelerate the evaluation process of obtaining accurate and converged thermal conductivity. Secondly, a microscopic picture is established from the fundamental level of electronic structure, which explains the mechanism underlying the phononan harmonicity in phosphorene and a class of 2D materials based on the basic principles of resonant bonds and lone-pair electrons. To the best of our knowledge, for the first time the resonant bonding and lone-pair electrons in 2D material are found to be responsible for strong phonon anharmonicity and low thermal conductivity. Thirdly, the thermal transport properties of two novel materials of monolayergallium nitride and monolayer carbon nitride are studied. In particular, we report that, despite the commonly established 1=T relation of thermal conductivity in plenty of materials, anomalous behavior emerges that the thermal conductivity almost decreases linearly over a wide temperature range above 300 K, deviating largely from the traditional 1=T law. The thermal conductivity at high temperature is much larger than the expected thermal conductivity that follows the general 1=T trend, which would be beneficial for their applications in nano and opto-electronics in terms of efficient heat dissipation. Finally, we investigate how the phonon transport can be manipulated by applying external electric field, strain, and bond nano designing. The study cases are 2D silicene, group III-nitrides, and boron arsenide (BAs). We demonstrate that the in-plane heat conduction of silicone can be dramatically regulated by simply applying out-of-plane electric field, without altering the atomic structure. Fundamental insights into the governing mechanism are achieved from the view of electronic structures. Comparing with existing methods, our study offers a new and robust way to modulate phonon transport in solids without altering the atomic structure, with great potential for applications in emerging fields, such as thermal managements, nano-electronics, and thermoelectrics. Moreover, we perform a comparative study of thermal transport in graphene and monolayer group III-nitrides combining with other similar representative 2D compounds. All these 2D materials share similar planar honeycomb structure. However, the thermal conductivity of all monolayer compounds is unexpectedly enlarged by up to one order of magnitude with bilateral tensile strain applied, which is in sharp contrast to the strain induced reduction in graphene. The underlying mechanism for the anomalous positive response of to tensile strain can be well understood based on the established microscopic picture of the lone-pair electrons driving strong phonon anharmonicity. At the end, we performa systematic study on the thermal transport properties of graphene-like g-BAs, in comparison with cubic c-BAs, diamond, and graphene. The of g-BAs is found anomalously low, despite the similarity of the transformation from 3D cubic to 2Dhoneycomb planar geometry structures (c-BAs!g-BAs vs. diamond!graphene),which shows that cutting into nanoscale could be an effective approach for realizing low . Summary and outlook are placed at the end of the thesis.