Improving Graphene-metal Contacts: Thermal Induced Polishing
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Improving Graphene-metal Contacts: Thermal Induced Polishing Eliezer Fernando Oliveira1,2, Ricardo Paupitz Santos3, Pedro Alves da Silva Autreto1,4, Stanislav Moshkalev5, and Douglas Soares Galvão1,2 1
Gleb Wataghin Institute of Physics, Universidade Estadual de Campinas, Campinas, SP, Brazil
2
Center for Computational Engineering & Sciences (CCES), University of Campinas - UNICAMP, Campinas, SP, Brazil 3
Institute of Geosciences and Exact Sciences, São Paulo State University (UNESP), Rio Claro, SP, Brazil
4
Federal University of ABC, Center of Natural Human Science, Santo Andre, SP, Brazil
5
Center for Semiconductor Components, State University of Campinas (UNICAMP), Campinas, SP,
Brazil
ABSTRACT
Graphene is a very promising material for nanoelectronics applications due to its unique and remarkable electronic and thermal properties. However, when deposited on metallic electrodes the overall thermal conductivity is significantly decreased. This phenomenon has been attributed to the mismatch between the interfaces and contact thermal resistance. Experimentally, one way to improve the graphene/metal contact is through high-temperature annealing, but the detailed mechanisms behind these processes remain unclear. In order to address these questions, we carried out fully atomistic reactive molecular dynamics simulations using the ReaxFF force field to investigate the interactions between multi-layer graphene and metallic electrodes (nickel) under (thermal) annealing. Our results show that the annealing induces an upward-downward movement of the graphene layers, causing a piledriver-like effect over the metallic surface. This graphene induced movements cause a planarization (thermal polishing-like effect) of the metallic surface, which results in the increase of the effective graphene/metal contact area. This can also explain the experimentally observed improvements of the thermal and electric conductivities.
INTRODUCTION Graphene application in thermal management in electronic devices is very promising, since its thermal conductivity achieves values up to 5.3x10 3 W/mK [1]. However, good graphene/metal electrodes interfaces have been difficult to achieve. The structural graphene/metal mismatch drastically reduces thermal conductivities due to poor thermal contacts between the graphene and the metallic electrodes. Experimentally, one employed to address this University, issue has been high-temperature annealing [2]. Downloaded approach from https://www.cambridge.org/core. Monash on 16 Jan 2018 at 17:15:14, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2018.66
When local annealing of a multi-layer graphene at high-temperature (T≥1000.0°C) is performed by a laser beam (Figure 1), it results in an improved thermal contact between graphene/metal interfaces; this could be achieved due to decreased rugosity of the metallic substrate. Despite that significant improvements in thermal conduction have been obtained in this way, the underlying
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