Thermal properties of graphene under tensile stress

TL;DR

This study investigates how tensile stress affects the thermal properties of graphene monolayers using path-integral molecular dynamics simulations, revealing quantum effects and changes in specific heat and expansion behavior.

Contribution

It provides a detailed analysis of the influence of tensile stress on graphene's thermal and structural properties, incorporating quantum effects through PIMD simulations.

Findings

Specific heat varies as T at low stress, T^2 at high stress.

Quantum effects are significant even above 300 K.

Differences between in-plane and real areas impact thermodynamic properties.

Abstract

Thermal properties of graphene display peculiar characteristics associated to the two-dimensional nature of this crystalline membrane. These properties can be changed and tuned in the presence of applied stresses, both tensile and compressive. Here we study graphene monolayers under tensile stress by using path-integral molecular dynamics (PIMD) simulations, which allows one to take into account quantization of vibrational modes and analyze the effect of anharmonicity on physical observables. The influence of the elastic energy due to strain in the crystalline membrane is studied for increasing tensile stress and for rising temperature (thermal expansion). We analyze the internal energy, enthalpy, and specific heat of graphene, and compare the results obtained from PIMD simulations with those given by a harmonic approximation for the vibrational modes. This approximation turns out to be precise at low temperatures, and deteriorates as temperature and pressure are increased. At low temperature the specific heat changes as $c_p \sim T$ for stress-free graphene, and evolves to a dependence $c_p \sim T^2$ as the tensile stress is increased. Structural and thermodynamic properties display nonnegligible quantum effects, even at temperatures higher than 300~K. Moreover, differences in the behavior of the in-plane and real areas of graphene are discussed, along with their associated properties. These differences show up clearly in the corresponding compressibility and thermal expansion coefficient.