Possible pair-graphene structures govern the thermodynamic properties of arbitrarily stacked few-layer graphene

Yong Sun,Tsuyoshi Takase,Daichi Eto,Kenta Kirimoto,Shota Tsuru,Shohei Yoshimura

doi:10.1038/s41598-021-02995-5

Abstract

The thermodynamic properties of few-layer graphene arbitrarily stacked on LiNbO3 crystal were characterized by measuring the parameters of a surface acoustic wave as it passed through the graphene/LiNbO3 interface. The parameters considered included the propagation velocity, frequency, and attenuation. Mono-, bi-, tri-, tetra-, and penta-layer graphene samples were prepared by transferring individual graphene layers onto LiNbO3 crystal surfaces at room temperature. Intra-layer lattice deformation was observed in all five samples. Further inter-layer lattice deformation was confirmed in samples with odd numbers of layers. The inter-layer lattice deformation caused stick–slip friction at the graphene/LiNbO3 interface near the temperature at which the layers were stacked. The thermal expansion coefficient of the deformed few-layer graphene transitioned from positive to negative as the number of layers increased. To explain the experimental results, we proposed a few-layer graphene even–odd layer number stacking order effect. A stable pair-graphene structure formed preferentially in the few-layer graphene. In even-layer graphene, the pair-graphene structure formed directly on the LiNbO3 substrate. Contrasting phenomena were noted with odd-layer graphene. Single-layer graphene was bound to the substrate after the stable pair-graphene structure was formed. The pair-graphene structure affected the stacking order and inter-layer lattice deformation of few-layer graphene substantially.

Highlights

The thermodynamic properties of few-layer graphene arbitrarily stacked on LiNbO3 crystal were characterized by measuring the parameters of a surface acoustic wave as it passed through the graphene/LiNbO3 interface
Few-layer graphene, a two-dimensional (2D) carbon material with atomic thickness, has a negative in-plane thermal expansion coefficient (TEC) due to both graphene sheet rippling[1,2,3,4] and increasing phonon out-of-plane vibrations[5,6,7]. This negative TEC results in many challenges in the area of electronic devices because 2D carbon materials generally require a 3D material as a substrate and most 3D materials such as Si, S iO2, and SiC have positive TECs near room temperature. These diametrically opposite temperature coefficients often lead to residual thermal stress at the 2D/3D material interface, which greatly affects the electrical properties of the 2D carbon material and leads to instability regarding the characteristics of the resulting electronic devices
Other experimental results have showed that negative graphene TECs are related to in-plane contractions of ripples and wrinkles in the graphene layer[5,23,24] Recently, molecular dynamics (MD) simulations showed that graphene origami structures obtained via pattern-based surface functionalization provide TECs that are tunable from large negative values such as − 465 × 1 0−6 to large positive values such as + 33 × 10−6 K−1 between 250 and 350 K25

Summary

Introduction

The thermodynamic properties of few-layer graphene arbitrarily stacked on LiNbO3 crystal were characterized by measuring the parameters of a surface acoustic wave as it passed through the graphene/LiNbO3 interface. Few-layer graphene, a two-dimensional (2D) carbon material with atomic thickness, has a negative in-plane thermal expansion coefficient (TEC) due to both graphene sheet rippling[1,2,3,4] and increasing phonon out-of-plane vibrations[5,6,7]. This negative TEC results in many challenges in the area of electronic devices because 2D carbon materials generally require a 3D material as a substrate and most 3D materials such as Si, S iO2, and SiC have positive TECs near room temperature. Many challenges remain regarding evaluation of the thermodynamic properties of such deformed few-layer graphene

Methods

Results

Conclusion