First principle study of the thermal conductance in graphene nanoribbon with vacancy and substitutional silicon defect

TL;DR

This study uses first-principles calculations and NEGF formalism to analyze how vacancies and silicon defects affect thermal conductance in graphene nanoribbons, revealing position-dependent effects of vacancies.

Contribution

It introduces an efficient correction method for force constants in first-principles NEGF calculations of defective graphene nanoribbons.

Findings

Vacancy position greatly influences thermal conductance.

Center vacancies cause significant phonon scattering and reduce conductance.

Silicon defect position has negligible impact on conductance.

Abstract

The thermal conductance in graphene nanoribbon with a vacancy or silicon point defect (substitution of C by Si atom) is investigated by non-equilibrium Green's function (NEGF) formalism combined with first-principle calculations density-functional theory with local density approximation. An efficient correction to the force constant matrix is presented to solve the conflict between the long-range character of the {\it ab initio} approach and the first-nearest-neighboring character of the NEGF scheme. In nanoribbon with a vacancy defect, the thermal conductance is very sensitive to the position of the vacancy defect. A vacancy defect situated at the center of the nanoribbon generates a saddle-like surface, which greatly reduces the thermal conductance by strong scattering to all phonon modes; while an edge vacancy defect only results in a further reconstruction of the edge and slightly reduces the thermal conductance. For the Si defect, the position of the defect plays no role for the value of the thermal conductance, since the defective region is limited within a narrow area around the defect center.